Possible Issue #1 fix

Don't need the switch with the fall-through; canPlayVideo() gives a nicer test as to whether the browser can play the video, and if it can't, it doesn't append the video to the dom, it just uses a gif.

A further possibility is a check on whether or not to add the shadow root, where if videos are unsupported, just default to adding an img.
Merge pull request #3 from mrecachinas/master

Possible Issue #1 fix