Fix compatibility with Rails 4.1.0.rc1 since it no longer autoloads FileSystemResolver in action_view.rb

Forward-porting a require statement to load FileSystemResolver
* This fixes haml_coffee_assets-1.16.0/lib/haml_coffee_assets/action_view/resolver.rb:9:in `<module:ActionView>': uninitialized constant ActionView::FileSystemResolver (NameError)
* For more details, see rails @ 3fbff7811bc7142e6f4142f807dd7b6ebd766a13 (https://github.com/rails/rails/commit/3fbff7811bc7142e6f4142f807dd7b6ebd766a13#diff-90f6f2b6859f5da65e11631ebcdf3f09)