Update _animFrame with me.sys.useNativeAnimFrame enabled.
Update _animFrame with me.sys.useNativeAnimFrame enabled.

- Fixes me.sys.pauseOnBlur with me.sys.useNativeAnimFrame enabled.
- Fixes a case where the game state would update faster and faster every time me.state.change() is called.

TukekeSoft/melonJS,Smoss/Enoru-eco,TukekeSoft/melonJS,MarkoIvanetic/melonJS,gopalindians/melonJS,srbala/melonJS,Smoss/Enoru-eco,srbala/melonJS,srbala/melonJS,melonjs/melonJS,rlugojr/melonJS,rlugojr/melonJS,gopalindians/melonJS,rlugojr/melonJS,melonjs/melonJS,MarkoIvanetic/melonJS,gopalindians/melonJS,TukekeSoft/melonJS