'Self signed certificate' error during query the Heroku hosted Postgres database from the Node.js application

My Node.js app is able to work with local Postgres database via npm pg module. I can connect to the Heroku hosted Postgres database (free Hobby Dev plan) via command line with heroku pg:psql command as well. But when my Node.js app is trying to query to Heroku hosted Postgres database I am receiving an self signed certificate error.

Here is the output with self signed certificate error:

(node:2100) UnhandledPromiseRejectionWarning: Error: self signed certificate
    at TLSSocket.onConnectSecure (_tls_wrap.js:1051:34)
    at TLSSocket.emit (events.js:189:13)
    at TLSSocket._finishInit (_tls_wrap.js:633:8)
(node:2100) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 1)
(node:2100) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.
D:\MY\DEV\PROJECTS\AdsSubscribeBot\test.js:57
  if (err) throw err;
           ^

Error: Connection terminated unexpectedly
    at Connection.con.once (D:\MY\DEV\PROJECTS\AdsSubscribeBot\node_modules\pg\lib\client.js:264:9)
    at Object.onceWrapper (events.js:277:13)
    at Connection.emit (events.js:189:13)
    at Socket.<anonymous> (D:\MY\DEV\PROJECTS\AdsSubscribeBot\node_modules\pg\lib\connection.js:76:10)
    at Socket.emit (events.js:194:15)
    at TCP._handle.close (net.js:597:12)

Simpliest way to reproduce this error is to try use the sample code to connecting in Node.js from Heroku devcenter: https://devcenter.heroku.com/articles/heroku-postgresql#connecting-in-node-js

Here is the sample of the code that causes self signed certificate error:

const connectionString = 'postgres://USERNAME:PASSWORD@HOST:PORT/DB_NAME';

const { Client } = require('pg');

const client = new Client({
  connectionString: connectionString,
  ssl: true
});

client.connect();

client.query('SELECT * FROM users;', (err, res) => {
  if (err) throw err;
  for (let row of res.rows) {
    console.log(JSON.stringify(row));
  }
  client.end();
});

Maybe someone has faced the same issue and know the way how to solve it.

Thanks in advance for any help.