title: Http Server upgrade event not being called on Heroku servers
body: <p>Why 'upgrade' event is not being called on Heroku servers?</p>
  
  <pre><code>var server = new http.Server();
  
  server.on('upgrade', function(req, socket, upgradeHead) {
      // ...
  });
  </code></pre>
  
  <p>Instead, the 'request' event is being called.</p>
  
  <p>I am running the same script in my local machine and with websocket requests the upgrade events is being called.</p>
  
  <p>Is it forbidden?</p>
  
  <p>Thanks.</p>