Update Video.JS to 4.8.1

In this pull request i will update the plugin to Video.JS version 4.8.1. It won't be backward compatible.

I updated Video.JS already in the **demo/** directory, so it can be tested.

Fixes:
* Features API has changed, but was fixed

TODO:
* When the player stops casting, Video.JS is changing to the native HTML5 player. The error message that appears is `Failed to set the 'currentTime' property on 'HTMLM…ement': The element's readyState is HAVE_NOTHING.`.