Fix I18n.enforce_available_locales warning

The warning message was:

  [deprecated] I18n.enforce_available_locales will default to true in
  the future. If you really want to skip validation of your locale you
  can set I18n.enforce_available_locales = false to avoid this message.

spec/spec_helper.rb

@@ -24,3 +24,5 @@ RSpec.configure do |config|
   config.include Shoulda::Matchers::ActionController,
                  example_group: { file_path: /action_controller/ }
 end
+
+I18n.enforce_available_locales = false