Loosen Bourne dependency to ~> 1.3

> Use a pessimistic version in the Gemfile for gems that follow semantic
> versioning, such as rspec, factory_girl, and capybara.

https://github.com/thoughtbot/guides/tree/master/best-practices

* Upgrade dependencies so specs run on new Bourne.
* Use semantic versions in step_definitions gems.
* Rely on ActiveSupport::Dependencies.clear for reloading constants.
  http://rkh.im/code-reloading
Drop Ruby 1.8.7 support