DeprecationWarning: current Server Discovery and Monitoring engine is deprecate

I cannot get rid of the warning. My code:

const MongoClient = require('mongodb').MongoClient;

let app = {};
const config = require('../config')(app);

const appl = async() => {
  const url = config.dbConnector;
  console.log(url);
  const client = new MongoClient(url, {
    useUnifiedTopology: true,
  });
  await client.connect();
  const db = client.db('zcloud');
  const appusers = await db.collection('AppUser').find().toArray();
  appusers.forEach((u) => {
    console.log(u.userId);
  });
}

appl().then(() => {
  process.exit(0);
}).catch((err) => {
  console.log(err);
  process.exit(1);
});

I get
(node:87168) DeprecationWarning: current Server Discovery and Monitoring engine is deprecated, and will be removed in a future version. To use the new Server Discover and Monitoring engine, pass option { useUnifiedTopology: true } to the MongoClient constructor.