Add license from raf polyfill

Author: rreusser

src/lib/request_animation_frame.js

@@ -6,6 +6,15 @@
 * LICENSE file in the root directory of this source tree.
 */
 
+// This code adapted from:
+//
+// http://paulirish.com/2011/requestanimationframe-for-smart-animating/
+// http://my.opera.com/emoller/blog/2011/12/20/requestanimationframe-for-smart-er-animating
+
+// requestAnimationFrame polyfill by Erik Möller. fixes from Paul Irish and Tino Zijdel
+
+// MIT license
+
 
 'use strict';