Fix Rails 5 deprecation warning for skip_before_action

DEPRECATION WARNING:

`skip_before_filter` is deprecated and will be removed in Rails 5.1. Use
`skip_before_action` instead.

Author: csexton

spec/dummy/app/controllers/welcome_controller.rb

@@ -1,5 +1,5 @@
 class WelcomeController < ApplicationController
-  skip_before_filter :authenticate_user!, only: [:index]
+  skip_before_action :authenticate_user!, only: [:index]
 
   def index
   end