fix for carrierwave

CarrierWave doesn't have 'do_not_validate_attachment_file_type' method.

rails s
=> Booting Thin
=> Rails 4.0.3 application starting in development on http://0.0.0.0:3000
=> Run `rails server -h` for more startup options
=> Ctrl-C to shutdown server
Exiting
/Users/marcinadamczyk/.rvm/gems/ruby-2.1.1@selena/gems/activerecord-4.0.3/lib/active_record/dynamic_matchers.rb:22:in `method_missing': undefined method `do_not_validate_attachment_file_type' for Rich::RichFile(no database connection):Class (NoMethodError)