It doesn't actually depend on rails, just railties

This allows an application not to download the activerecord and arel gems for instance, if they don't use such ORM. As long as the application itself doesn't depend on the rails gem but railties instead.
sprockets-rails is also another dependency besides railties
rails40 application doesn't need explicit dependency on tzinfo
Merge pull request #97 from rosenfeld/patch-1

It doesn't actually depend on rails, just railties