Rename filter method.

I don't know when this changed:

"The filter class must implement a method with the same name as the filter, so for the before_action filter the class must implement a before method, and so on."

http://guides.rubyonrails.org/action_controller_overview.html
Merge pull request #2 from juanibiapina/patch-1

Rename "filter" method.to "before" in controller filter class.

This is likely to be a recent change in Rails.