How to use the bottender.ViberBot function in bottender

const server = express();

server.use(
  bodyParser.json({
    verify: (req, res, buf) => {
      req.rawBody = buf.toString();
    },
  })
);

const bots = {
  messenger: new MessengerBot(config.messenger).onEvent(handler),
  line: new LineBot(config.line).onEvent(handler),
  slack: new SlackBot(config.slack).onEvent(handler),
  telegram: new TelegramBot(config.telegram).onEvent(handler),
  viber: new ViberBot(config.viber).onEvent(handler),
};

registerRoutes(server, bots.messenger, {
  path: '/messenger',
  verifyToken: config.messenger.verifyToken,
});
registerRoutes(server, bots.line, { path: '/line' });
registerRoutes(server, bots.slack, { path: '/slack' });
registerRoutes(server, bots.telegram, { path: '/telegram' });
registerRoutes(server, bots.viber, { path: '/viber' });

server.listen(5000, () => {
  console.log('server is listening on 5000 port...');
});

const { ViberBot, ViberHandler } = require('bottender');
const { createServer } = require('bottender/express');

const config = require('./bottender.config').viber;

const bot = new ViberBot({
  accessToken: config.accessToken,
});

const handler = new ViberHandler()
  .onDelivered(() => {
    console.log('delivered');
  })
  .onSeen(() => {
    console.log('seen');
  })
  .onFailed(() => {
    console.log('failed');
  })
  .onText(/yo/i, async context => {
    await context.sendText('Hi there!');
  })