Update Rails to 4.2.0

config/application.rb

@@ -20,5 +20,8 @@ module Projekteuler
     config.i18n.load_path += Dir[Rails.root.join('config', 'locales', '**', '*.{rb,yml}').to_s]
     config.i18n.available_locales = :de
     config.i18n.default_locale = :de
+
+    # Do not swallow errors in after_commit/after_rollback callbacks.
+    config.active_record.raise_in_transactional_callbacks = true
   end
 end