Added GogsHookUpdate in import

Author: Costin Bleotu

gogs_client/__init__.py

@@ -1,4 +1,4 @@
 from gogs_client.auth import Authentication, Token, UsernamePassword
 from gogs_client.entities import GogsUser, GogsRepo
 from gogs_client.interface import GogsApi, ApiFailure, NetworkFailure
-from gogs_client.updates import GogsUserUpdate
+from gogs_client.updates import GogsUserUpdate, GogsHookUpdate