message: fix reference to dialogset
diff: @@ -385,7 +385,7 @@ onboarding.after(async(results, bot) => {
  });
  // add the conversation to the dialogset
  -controller.dialogSet.add(onboarding);
  +controller.addDialog(onboarding);
  // launch the dialog in response to a message or event
  controller.hears(['hello'], 'message', async(bot, message) => {
  @@ -451,7 +451,7 @@ controller.ready(() => {
  ### Native Bot Builder Dialogs
  -[BotBuilder dialogs](https://npmjs.com/package/botbuilder-dialogs) can live alongside Botkit! Define dialogs using `WaterfallDialogs`, `ComponentDialogs`, or your own derived dialog class. Then, make them available for your bot to use by calling `controller.dialogSet.add()`:
  +[BotBuilder dialogs](https://npmjs.com/package/botbuilder-dialogs) can live alongside Botkit! Define dialogs using `WaterfallDialogs`, `ComponentDialogs`, or your own derived dialog class. Then, make them available for your bot to use by calling `controller.addDialog()`:
  [Read about BotBuilder dialogs in Microsoft's official documentation &rarr;](https://docs.microsoft.com/en-us/azure/bot-service/bot-builder-concept-dialog?view=azure-bot-service-4.0)
  @@ -469,7 +469,7 @@ const myWelcomeDialog = new WaterfallDialog('welcome', [
  }
  ]);
  -controller.dialogSet.add(myWelcomeDialog);
  +controller.addDialog(myWelcomeDialog);
  ```
  In order to trigger the dialog from within a Botkit handler function, call `await bot.beginDialog('dialog_id');` as below:
  