Use spermy version specifier. Fix specs.

It's better to use `~>` version specifier. It allows to avoid breaking when new major version of dependencies are released.
You can [read more](http://stackoverflow.com/questions/3492772/gem-dependencies-versions-meaning) about it.

Also removed `size.should == n` asserts. Since some tests relies on tests which should be ran before and it makes them broken. At least they doesn't pass with RSpec 2.11.0

However I still have one test broken on my environment(rails 3.2.6, ruby 1.9.3-p194).

```

  1) HasTokenOn::Base when setting the token should generate GUID using SimpleUUID if it is available
     Failure/Error: subject.save
     ArgumentError:
       wrong number of arguments (0 for 2..3)
     # .rvm/gems/ruby-1.9.3-p194/gems/activemodel-3.2.6/lib/active_model/dirty.rb:143:in `test'
     # .rvm/gems/ruby-1.9.3-p194/gems/activemodel-3.2.6/lib/active_model/dirty.rb:143:in `attribute_change'
     # .rvm/gems/ruby-1.9.3-p194/gems/activemodel-3.2.6/lib/active_model/dirty.rb:117:in `block in changes'
     # .rvm/gems/ruby-1.9.3-p194/gems/activemodel-3.2.6/lib/active_model/dirty.rb:117:in `map'
     # .rvm/gems/ruby-1.9.3-p194/gems/activemodel-3.2.6/lib/active_model/dirty.rb:117:in `changes'
     # .rvm/gems/ruby-1.9.3-p194/gems/activerecord-3.2.6/lib/active_record/attribute_methods/dirty.rb:23:in `save'
     # .rvm/gems/ruby-1.9.3-p194/gems/activerecord-3.2.6/lib/active_record/transactions.rb:241:in `block (2 levels) in save'
     # .rvm/gems/ruby-1.9.3-p194/gems/activerecord-3.2.6/lib/active_record/transactions.rb:295:in `block in with_transaction_returning_status'
     # .rvm/gems/ruby-1.9.3-p194/gems/activerecord-3.2.6/lib/active_record/connection_adapters/abstract/database_statements.rb:192:in `transaction'
     # .rvm/gems/ruby-1.9.3-p194/gems/activerecord-3.2.6/lib/active_record/transactions.rb:208:in `transaction'
     # .rvm/gems/ruby-1.9.3-p194/gems/activerecord-3.2.6/lib/active_record/transactions.rb:293:in `with_transaction_returning_status'
     # .rvm/gems/ruby-1.9.3-p194/gems/activerecord-3.2.6/lib/active_record/transactions.rb:241:in `block in save'
     # .rvm/gems/ruby-1.9.3-p194/gems/activerecord-3.2.6/lib/active_record/transactions.rb:252:in `rollback_active_record_state!'
     # .rvm/gems/ruby-1.9.3-p194/gems/activerecord-3.2.6/lib/active_record/transactions.rb:240:in `save'
     # ./spec/has_token_on/base_spec.rb:189:in `block (3 levels) in <top (required)>'
     # .rvm/gems/ruby-1.9.3-p194/gems/rspec-core-2.11.0/lib/rspec/core/example.rb:113:in `instance_eval'
     # .rvm/gems/ruby-1.9.3-p194/gems/rspec-core-2.11.0/lib/rspec/core/example.rb:113:in `block in run'
     # .rvm/gems/ruby-1.9.3-p194/gems/rspec-core-2.11.0/lib/rspec/core/example.rb:253:in `with_around_each_hooks'
     # .rvm/gems/ruby-1.9.3-p194/gems/rspec-core-2.11.0/lib/rspec/core/example.rb:110:in `run'
     # .rvm/gems/ruby-1.9.3-p194/gems/rspec-core-2.11.0/lib/rspec/core/example_group.rb:378:in `block in run_examples'
     # .rvm/gems/ruby-1.9.3-p194/gems/rspec-core-2.11.0/lib/rspec/core/example_group.rb:374:in `map'
     # .rvm/gems/ruby-1.9.3-p194/gems/rspec-core-2.11.0/lib/rspec/core/example_group.rb:374:in `run_examples'
     # .rvm/gems/ruby-1.9.3-p194/gems/rspec-core-2.11.0/lib/rspec/core/example_group.rb:360:in `run'
     # .rvm/gems/ruby-1.9.3-p194/gems/rspec-core-2.11.0/lib/rspec/core/example_group.rb:361:in `block in run'
     # .rvm/gems/ruby-1.9.3-p194/gems/rspec-core-2.11.0/lib/rspec/core/example_group.rb:361:in `map'
     # .rvm/gems/ruby-1.9.3-p194/gems/rspec-core-2.11.0/lib/rspec/core/example_group.rb:361:in `run'
     # .rvm/gems/ruby-1.9.3-p194/gems/rspec-core-2.11.0/lib/rspec/core/command_line.rb:28:in `block (2 levels) in run'
     # .rvm/gems/ruby-1.9.3-p194/gems/rspec-core-2.11.0/lib/rspec/core/command_line.rb:28:in `map'
     # .rvm/gems/ruby-1.9.3-p194/gems/rspec-core-2.11.0/lib/rspec/core/command_line.rb:28:in `block in run'
     # .rvm/gems/ruby-1.9.3-p194/gems/rspec-core-2.11.0/lib/rspec/core/reporter.rb:34:in `report'
     # .rvm/gems/ruby-1.9.3-p194/gems/rspec-core-2.11.0/lib/rspec/core/command_line.rb:25:in `run'
     # .rvm/gems/ruby-1.9.3-p194/gems/rspec-core-2.11.0/lib/rspec/core/runner.rb:69:in `run'
     # .rvm/gems/ruby-1.9.3-p194/gems/rspec-core-2.11.0/lib/rspec/core/runner.rb:8:in `block in autorun'

```

Could you please help me to figure out what's wrong?