Catch more type of error from Firebase

[fgarzonhz]

What version of PushSharp are you using?

4.0

Describe your issue:

Firebase return an error but using the code from the client only catch the words "unknow error"

in c#
P.pushGoogle2.OnNotificationFailed += (notification, aggregateEx) =>
{ aggregateEx.Handle(ex =>
{
console.write(ex.Message + " : " + ex.StackTrace.ToString()); //here only print "error"

What are the steps required to reproduce this issue?

Firebase return the error: {"multicast_id":99999999,"success":0,"failure":1,"canonical_ids":0,"results":[{"error":"InvalidApnsCredential"}]}

Please provide any Exception Stack Traces

I saw the pushsharp code and we need to add a new enum to catch InvalidApnsCredential (may suggestio in related in line 203 of file GCmServiceConnection.cs [ static GcmResponseStatus GetGcmResponseStatus (string str) ])