FIX: Add test to confirm updating category works.

Also replaces a missing translation key that 99.9% of users would never
see.

lib/reviewable/actions.rb

@@ -15,6 +15,7 @@ class Reviewable < ActiveRecord::Base
       {
         approve: Action.new(:approve, 'thumbs-up', 'reviewables.actions.approve.title'),
         reject: Action.new(:reject, 'thumbs-down', 'reviewables.actions.reject.title'),
+        delete: Action.new(:delete, 'trash-alt', 'reviewables.actions.delete_single.title')
       }
     end