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

Request Type: bug

How to reproduce: Load a page with Angular >= 1.2.14 and ngAnimate >= 1.2.14 on a old version of Firefox (20 for example)

Component(s): ngAnimate

Impact: small

Complexity: small

This issue is related to: 

**Detailed Description:**

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

**Other Comments:**

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