Update adapter.js / autoplay for webkit browsers

Video "freezes" in webkit (Chrome & Opera), but in fact the play() method is missing on (re)attachMediaStream.

EDIT:
From some discussion with @ns_schoe on twitter, I found out that setting autoplay to video element solve this issue.
So, there are two options: remove autoplay for moz and let user set this within html attribute or add my 2 lines to support webkit.