Get the test suite passing on Rails 4.1

The minitest addition was to get around this error:
```
Warning: you should require 'minitest/autorun' instead.
Warning: or add 'gem "minitest"' before 'require "minitest/autorun"'
```

The failures I got when running locally:
```
Failures:

  1) defining new actions from registration blocks generating a new member action with :title 
     Failure/Error: controller._process_action_callbacks.detect { |f| f.kind == :before && f.options[:only] == [action] }
     NoMethodError:
       undefined method `options' for #<ActiveSupport::Callbacks::Callback:0x00000106021690>
     # ./spec/unit/action_builder_spec.rb:112:in `block in find_before_filter'
     # ./spec/unit/action_builder_spec.rb:112:in `detect'
     # ./spec/unit/action_builder_spec.rb:112:in `find_before_filter'
     # ./spec/unit/action_builder_spec.rb:55:in `block (4 levels) in <top (required)>'
     # ./spec/unit/action_builder_spec.rb:57:in `block (4 levels) in <top (required)>'

  2) defining new actions from registration blocks generate a new collection action with :title 
     Failure/Error: controller._process_action_callbacks.detect { |f| f.kind == :before && f.options[:only] == [action] }
     NoMethodError:
       undefined method `options' for #<ActiveSupport::Callbacks::Callback:0x00000106021690>
     # ./spec/unit/action_builder_spec.rb:112:in `block in find_before_filter'
     # ./spec/unit/action_builder_spec.rb:112:in `detect'
     # ./spec/unit/action_builder_spec.rb:112:in `find_before_filter'
     # ./spec/unit/action_builder_spec.rb:105:in `block (4 levels) in <top (required)>'
     # ./spec/unit/action_builder_spec.rb:107:in `block (4 levels) in <top (required)>'

  3) ActiveAdmin::FormBuilder with has many inputs sortable with a new post shows the nested fields for unsaved records
     Failure/Error: f.has_many :posts, sortable: :position do |p|
     NoMethodError:
       undefined method `sort_by!' for #<Post::ActiveRecord_Associations_CollectionProxy:0x000001377d5630>
     # ./lib/active_admin/form_builder.rb:86:in `has_many'
     # ./spec/unit/form_builder_spec.rb:440:in `block (6 levels) in <top (required)>'
     # ./lib/active_admin/view_helpers/form_helper.rb:9:in `active_admin_form_for'
     # ./spec/unit/form_builder_spec.rb:36:in `block in build_form'
     # ./spec/spec_helper.rb:53:in `new'
     # ./spec/spec_helper.rb:53:in `arbre'
     # ./spec/spec_helper.rb:57:in `render_arbre_component'
     # ./spec/unit/form_builder_spec.rb:35:in `build_form'
     # ./spec/unit/form_builder_spec.rb:438:in `block (5 levels) in <top (required)>'
     # ./spec/unit/form_builder_spec.rb:447:in `block (5 levels) in <top (required)>'

  4) ActiveAdmin::FormBuilder with has many inputs sortable with post returning nil for the sortable attribute shows the nested fields for unsaved records
     Failure/Error: f.has_many :posts, sortable: :position do |p|
     NoMethodError:
       undefined method `sort_by!' for #<Post::ActiveRecord_Associations_CollectionProxy:0x000001377e18e0>
     # ./lib/active_admin/form_builder.rb:86:in `has_many'
     # ./spec/unit/form_builder_spec.rb:457:in `block (6 levels) in <top (required)>'
     # ./lib/active_admin/view_helpers/form_helper.rb:9:in `active_admin_form_for'
     # ./spec/unit/form_builder_spec.rb:36:in `block in build_form'
     # ./spec/spec_helper.rb:53:in `new'
     # ./spec/spec_helper.rb:53:in `arbre'
     # ./spec/spec_helper.rb:57:in `render_arbre_component'
     # ./spec/unit/form_builder_spec.rb:35:in `build_form'
     # ./spec/unit/form_builder_spec.rb:454:in `block (5 levels) in <top (required)>'
     # ./spec/unit/form_builder_spec.rb:464:in `block (5 levels) in <top (required)>'

  5) ActiveAdmin::FormBuilder with has many inputs sortable with existing and new posts shows the nested fields for saved and unsaved records
     Failure/Error: f.has_many :posts, sortable: :position do |p|
     NoMethodError:
       undefined method `sort_by!' for #<Post::ActiveRecord_Associations_CollectionProxy:0x00000138011420>
     # ./lib/active_admin/form_builder.rb:86:in `has_many'
     # ./spec/unit/form_builder_spec.rb:479:in `block (6 levels) in <top (required)>'
     # ./lib/active_admin/view_helpers/form_helper.rb:9:in `active_admin_form_for'
     # ./spec/unit/form_builder_spec.rb:36:in `block in build_form'
     # ./spec/spec_helper.rb:53:in `new'
     # ./spec/spec_helper.rb:53:in `arbre'
     # ./spec/spec_helper.rb:57:in `render_arbre_component'
     # ./spec/unit/form_builder_spec.rb:35:in `build_form'
     # ./spec/unit/form_builder_spec.rb:477:in `block (5 levels) in <top (required)>'
     # ./spec/unit/form_builder_spec.rb:486:in `block (5 levels) in <top (required)>'

  6) ActiveAdmin::Helpers::Collection#collection_size should return the collection size for an ActiveRecord class
     Failure/Error: expect(collection_size(Post.scoped)).to eq 3
     NoMethodError:
       undefined method `scoped' for #<Class:0x0000010a6145a8>
     # ./spec/unit/helpers/collection_spec.rb:20:in `block (3 levels) in <top (required)>'

  7) ActiveAdmin::Helpers::Collection#collection_size should return the collection size for a collection with group by, select and custom order
     Failure/Error: expect(collection_size(Post.select("title, count(*) as nb_posts").group(:title).order("nb_posts"))).to eq 2
     ActiveRecord::StatementInvalid:
       SQLite3::SQLException: near "as": syntax error: SELECT COUNT(title, count(*) as nb_posts) AS count_title_count_all_as_nb_posts, title AS title FROM "posts"  GROUP BY title
     # ./lib/active_admin/helpers/collection.rb:12:in `collection_size'
     # ./spec/unit/helpers/collection_spec.rb:32:in `block (3 levels) in <top (required)>'

  8) ActiveAdmin::Helpers::Collection#collection_size should take the defined collection by default
     Failure/Error: def collection; Post.scoped; end
     NoMethodError:
       undefined method `scoped' for #<Class:0x0000010a6145a8>
     # ./spec/unit/helpers/collection_spec.rb:36:in `collection'
     # ./lib/active_admin/helpers/collection.rb:10:in `collection_size'
     # ./spec/unit/helpers/collection_spec.rb:38:in `block (3 levels) in <top (required)>'

  9) ActiveAdmin::Helpers::Collection#collection_is_empty? should take the defined collection by default
     Failure/Error: def collection; Post.scoped; end
     NoMethodError:
       undefined method `scoped' for #<Class:0x0000010a6145a8>
     # ./spec/unit/helpers/collection_spec.rb:56:in `collection'
     # ./lib/active_admin/helpers/collection.rb:18:in `collection_is_empty?'
     # ./spec/unit/helpers/collection_spec.rb:58:in `block (3 levels) in <top (required)>'

  10) ActiveAdmin::ResourceController::Decorators#apply_collection_decorator when a decorator is configured and it is using a recent version of draper calling certain scope collections work
     Failure/Error: let(:collection) { Post.scoped }
     NoMethodError:
       undefined method `scoped' for #<Class:0x0000010a6145a8>
     # ./spec/unit/resource_controller/decorators_spec.rb:45:in `block (3 levels) in <top (required)>'
     # ./spec/unit/resource_controller/decorators_spec.rb:46:in `block (3 levels) in <top (required)>'
     # ./spec/unit/resource_controller/decorators_spec.rb:55:in `block (5 levels) in <top (required)>'

  11) ActiveAdmin::ResourceController::Decorators#apply_collection_decorator when a decorator is configured and it is using a recent version of draper has a good description for the generated class
     Failure/Error: let(:collection) { Post.scoped }
     NoMethodError:
       undefined method `scoped' for #<Class:0x0000010a6145a8>
     # ./spec/unit/resource_controller/decorators_spec.rb:45:in `block (3 levels) in <top (required)>'
     # ./spec/unit/resource_controller/decorators_spec.rb:46:in `block (3 levels) in <top (required)>'
     # ./spec/unit/resource_controller/decorators_spec.rb:59:in `block (5 levels) in <top (required)>'

  12) ActiveAdmin::ResourceController::Sidebars#skip_sidebar! should set skip sidebar to true
     Failure/Error: klass = filter && filter.klass || controller
     NoMethodError:
       undefined method `klass' for #<ActiveSupport::Callbacks::Callback:0x000001235f1670>
     # ./spec/unit/resource_controller/sidebars_spec.rb:35:in `block (3 levels) in <top (required)>'
     # ./spec/unit/resource_controller/sidebars_spec.rb:25:in `block (3 levels) in <top (required)>'

Finished in 13.81 seconds
974 examples, 12 failures, 15 pending

Failed examples:

rspec ./spec/unit/action_builder_spec.rb:57 # defining new actions from registration blocks generating a new member action with :title 
rspec ./spec/unit/action_builder_spec.rb:107 # defining new actions from registration blocks generate a new collection action with :title 
rspec ./spec/unit/form_builder_spec.rb:446 # ActiveAdmin::FormBuilder with has many inputs sortable with a new post shows the nested fields for unsaved records
rspec ./spec/unit/form_builder_spec.rb:463 # ActiveAdmin::FormBuilder with has many inputs sortable with post returning nil for the sortable attribute shows the nested fields for unsaved records
rspec ./spec/unit/form_builder_spec.rb:485 # ActiveAdmin::FormBuilder with has many inputs sortable with existing and new posts shows the nested fields for saved and unsaved records
rspec ./spec/unit/helpers/collection_spec.rb:19 # ActiveAdmin::Helpers::Collection#collection_size should return the collection size for an ActiveRecord class
rspec ./spec/unit/helpers/collection_spec.rb:31 # ActiveAdmin::Helpers::Collection#collection_size should return the collection size for a collection with group by, select and custom order
rspec ./spec/unit/helpers/collection_spec.rb:35 # ActiveAdmin::Helpers::Collection#collection_size should take the defined collection by default
rspec ./spec/unit/helpers/collection_spec.rb:55 # ActiveAdmin::Helpers::Collection#collection_is_empty? should take the defined collection by default
rspec ./spec/unit/resource_controller/decorators_spec.rb:52 # ActiveAdmin::ResourceController::Decorators#apply_collection_decorator when a decorator is configured and it is using a recent version of draper calling certain scope collections work
rspec ./spec/unit/resource_controller/decorators_spec.rb:58 # ActiveAdmin::ResourceController::Decorators#apply_collection_decorator when a decorator is configured and it is using a recent version of draper has a good description for the generated class
rspec ./spec/unit/resource_controller/sidebars_spec.rb:25 # ActiveAdmin::ResourceController::Sidebars#skip_sidebar! should set skip sidebar to true
```