title: Opentok's preferredResolution for subscriber doen't work
body: <p>I create opentok sessions on backend using <code>MediaMode.ROUTED</code> and create publisher object like this:</p>
  
  <pre><code>var publisherOptions =  {
      resolution: '1280x960',
      style: {
          nameDisplayMode: "on",
          buttonDisplayMode: "off"
      },
  };
  const el = createElement();
  publisher = OT.initPublisher(el, publisherOptions);
  </code></pre>
  
  <p>On the subscriber end I connect like this:</p>
  
  <pre><code>subscriberOptions = {
      insertMode: 'append',
      preferredResolution: {width: 320, height: 240},
      style: {
          buttonDisplayMode: 'off'
      }
  };
  subscriber = session.subscribe(event.stream, 'subscriber', subscriberOptions, function(error) {
       if (error) {
       console.log('There was an error publishing: ', error.name, error.message);
       }
   });
  </code></pre>
  
  <p>But the stream I recieve on subscriber is <code>1280x960</code>, should'nt it be <code>320x240</code>?</p>
  
  <p>Am I missing anything?</p>