* Added channel_id option to Android config ([spec](https://firebase.google.com/docs/reference/fcm/rest/v1/projects.messages#AndroidNotification))
1.3.5
Not secure
* [FIX] Adjust APS encoder in order to properly construct background push notification.
1.3.4
Not secure
* [FIX] Set properly attribute ``content-available`` for APNS payload. The attribute indicates that push notification should be considered [background](https://developer.apple.com/documentation/usernotifications/setting_up_a_remote_notification_server/pushing_background_updates_to_your_app).
1.3.3
Not secure
* [FIX] Use numeric representation for boolean attributes ``mutable-content`` and ``content-available``.
1.3.2
Not secure
* [FIX] Encode ``Aps`` message according to APNS [specification](https://developer.apple.com/documentation/usernotifications/setting_up_a_remote_notification_server/generating_a_remote_notification) * [FIX] Util ``cleanup_firebase_message`` to remove null values for dict object. * [CHORE] Update dependencies