Fix for GCM Push for 2.2.0+

[abdox2]

The GCM Push notification was working fine in 1.6.0, so i was wondering why?? i looked for the difference in the file GCM.js between 1.6.0 and the latest 2.2.1, i fin out that the push_id a random string in the function generateGCMPayload is not sended, so i added it and everthing is working again.

before :

function generateGCMPayload(coreData, timeStamp, expirationTime) {
var payloadData = {
'time': new Date(timeStamp).toISOString(),
'data': JSON.stringify(coreData)
};
...
}
after:

function generateGCMPayload(coreData, timeStamp, expirationTime) {
var pushId = cryptoUtils.newObjectId();
var payloadData = {
'time': new Date(timeStamp).toISOString(),
'push_id': pushId,
'data': JSON.stringify(coreData)
};
...
}

Thank you to look in to it

[flovilmart]

OK, I'll added back as I thought it was conflicting with the _PushStatus objectID

[wangmengyan95]

Fixes in #1168

[abdox2]

Thank you all. i love this project :)