videojs updates

Switching videojs-vast back to main repo (theonion/videojs-vast-plugin) and moving the adblock style fix to the videojs-contrib-ads plugin as it seems like a more suitable place for it.

Opened up two PRs for the fixes in our fork of videojs-contrib-ads:
https://github.com/videojs/videojs-contrib-ads/pull/37
https://github.com/videojs/videojs-contrib-ads/pull/38