Rails/FilePath

[awead]

The default has changed to prefer slashes over arguments:

https://github.com/rubocop-hq/rubocop-rails/blob/v2.4.2/lib/rubocop/cop/rails/file_path.rb

Our previous code used arguments. Niftany 0.6 uses the defaults, with slashes now the preferred style, but we can switch back to arguments. FWIW, we're sticking with arguments in Scholarsphere.