Rails 4

This change is likely unnecessary as ```Rails::Application::Railties.engines``` does exactly the same (see https://github.com/rails/rails/blob/4-0-stable/railties/lib/rails/engine/railties.rb#L12-14)

If it was not replaced for good reason (maybe caching?),  ```Rails::Application::Railties.engines``` should be preferred because of better future robustness