Rename ARTPushRegistererDelegate.didAblyPushRegistrationFail to ARTPushRegistererDelegate.didAblyPushUpdateFail

[ben-xD]

ARTPushRegistererDelegate is the delegate with 3 methods which are called back:

• didActivateAblyPush: called when activate succeeds or fails
• didDeactivateAblyPush: called when deactivate succeeds or fails
• didAblyPushRegistrationFail: called when updating Ably with new details fails. The point is, it is only called when updating ably (in an internal method called callUpdateFailedCallback), and not during "registration"/ activation.

Additional, this is the same 3 APIs on Android, which are called. On Android, they are 3 intents which are created. The user has to listen to these:

• io.ably.broadcast.PUSH_ACTIVATE
• io.ably.broadcast.PUSH_DEACTIVATE
• io.ably.broadcast.PUSH_UPDATE_FAILED

Therefore, to allow users to understand the API better and make it appear consistent with Android, we should rename this method ARTPushRegistererDelegate.didAblyPushRegistrationFail to ARTPushRegistererDelegate.didAblyPushUpdateFail