Update Push Library to support Google's new API

"GCM register() is deprecated starting May 28, 2015. New app development should use the Instance ID API to handle the creation, rotation, and updating of registration tokens. If you need to troubleshoot legacy systems using code>register(), see Obtaining Registration Tokens with gcm.register()."

AG PUSH Library should be updated ASAP to support this

https://developers.google.com/cloud-messaging/registration