fix (ngAnimate): fix requestAnimationFrame for old version of Firefox

The recent $$RAFProvider which is a wrapper for the native
requestAnimationFrame method doesn't use the mozRequestAnimationFrame.
Old versions of FF (20 for example) crash if ngAnimate is included

No breaking changes and fix issue https://github.com/angular/angular.js/issues/6535

Closes #6535
Closes #6540