Removing redundant prefixes

According to [caniuse](http://caniuse.com/#search=requestanimationframe), there have never been `ms` and `o` prefixes for requestAnimationFrame.

I'd even go as far as to drop `moz` & `webkit`. They cover only 3% of old browsers which would than just use setTimeout fallback, but except cleaning the code there is no other reason to drop them. Thoughts?