Don't remove vjs-waiting until time changes

[gesinger]

Description

Sometimes the vjs-waiting class is removed prematurely after the player gets into a waiting state. This removes the graphic waiting spinner while the player is still waiting. To see this behavior on Chrome:

1. Go to https://videojs.github.io/http-streaming/
2. Open the console
3. Enter:

player.on('waiting', () => console.log('waiting'));
player.on('timeupdate', () => console.log('timeupdate: ' + player.currentTime()));
player.play();

4. Click "Offline" in the network tab

The console logs timeupdate events of the same time sandwiching a waiting event, e.g.:

...
timeupdate: 49.675262
timeupdate: 49.812381
waiting
timeupdate: 49.812381

Specific Changes proposed

This PR waits to remove the vjs-waiting class until the time changes on timeupdate events.

Requirements Checklist

• Feature implemented / Bug fixed
• If necessary, more likely in a feature request than a bug fix
  • Change has been verified in an actual browser (Chome, Firefox, IE)
  • Unit Tests updated or fixed
  • Docs/guides updated
  • Example created (starter template on JSBin)
• Reviewed by Two Core Contributors