message: update sample code to include restify-friendly verification endpoint
diff: @@ -58,6 +58,9 @@ controller.on('message', async(bot, message) => {
  Alternately, developers may choose to use `FacebookAdapter` with BotBuilder. With BotBuilder, the adapter is used more directly with a webserver, and all incoming events are handled as [Activities](https://docs.microsoft.com/en-us/javascript/api/botframework-schema/activity?view=botbuilder-ts-latest).
  ```javascript
  +const { FacebookAdapter } = require('botbuilder-adapter-facebook');
  +const restify = require('restify');
  +
  const adapter = new FacebookAdapter({
  verify_token: process.env.FACEBOOK_VERIFY_TOKEN,
  app_secret: process.env.FACEBOOK_APP_SECRET,
  @@ -65,11 +68,29 @@ const adapter = new FacebookAdapter({
  });
  const server = restify.createServer();
  server.use(restify.plugins.bodyParser());
  +server.use(restify.plugins.queryParser());
  +
  +server.get('/api/messages', (req, res) => {
  + if (req.query['hub.mode'] === 'subscribe') {
  + if (req.query['hub.verify_token'] === process.env.FACEBOOK_VERIFY_TOKEN) {
  + const val = req.query['hub.challenge'];
  + res.sendRaw(200, val);
  + } else {
  + console.log('failed to verify endpoint');
  + res.send('OK');
  + }
  + }
  +});
  +
  server.post('/api/messages', (req, res) => {
  adapter.processActivity(req, res, async(context) => {
  await context.sendActivity('I heard a message!');
  });
  });
  +
  +server.listen(process.env.port || process.env.PORT || 3000, () => {
  + console.log(`\n${ server.name } listening to ${ server.url }`);
  + });
  ```
  ### Multi-page Support
  