Specify sass-rails version in Gemfile

Fixes https://github.com/thoughtbot/suspenders/pull/325

Bundler could not find compatible versions for gem "sprockets":
  In Gemfile:
    sass-rails (>= 0) ruby depends on
      sprockets (~> 2.0.0) ruby

    rails (~> 4.1.0) ruby depends on
      sprockets-rails (~> 2.0) ruby depends on
        sprockets (2.12.1)

Bundler could not find compatible versions for gem "sprockets-rails":
  In Gemfile:
    sass-rails (>= 0) ruby depends on
      sprockets-rails (~> 2.0.0) ruby

    rails (~> 4.1.0) ruby depends on
      sprockets-rails (2.1.3)

Bundler could not find compatible versions for gem "railties":
  In Gemfile:
    sass-rails (>= 0) ruby depends on
      railties (~> 3.1.0) ruby

    rails (~> 4.1.0) ruby depends on
      railties (4.1.0)
Bump to 1.10.1
Specify Version Requirements for Bourbon and Neat

This resolves a sass version requirement conflict with sass-rails. These version
requirements should be removed or updated once sass-rails supports sass 3.3.

This pull request closes #328 on https://github.com/thoughtbot/suspenders.
Bump to 1.10.2
Improve and document TravisCI configuration

* Add Travis to README.
* Color the RSpec output.
* Create Postgres database.
* Set up xvfb for Capybara Webkit.
* Turn off email notifications.
* Remove unnecessary `ruby-` prefix to Ruby version.
* Use consistent formatting.
Add `bin/setup` for contributors

* Use `mkdir .git/safe` convention in `bin/setup`.
  https://github.com/thoughtbot/suspenders/commit/2ec7108
* Add missing `rake` binstub to version control.
* Update and improve `CONTRIBUTING.md`.
shoulda-matchers spring compatibility.

Changed Gemfile and spec_helper according to the shoulda-matchers
documentation:

Gemfile:

group :test do
  gem 'shoulda-matchers', require: false
end

spec_helper:

require 'rspec/rails'
require 'shoulda/matchers'u