message: Add missing `fallback` in example.
diff: @@ -854,6 +854,7 @@ controller.hears('interactive', 'direct_message', function(bot, message) {
  attachments:[
  {
  title: 'Do you want to interact with my buttons?',
  + fallback: 'You need the Slack app to interact with these buttons',
  callback_id: '123',
  attachment_type: 'default',
  actions: [
  