Fix repeatable filter assignment

Fix runtime error during filter assignment on a repeatable grpc field

Author: christmoore

etcd3/watch.py

@@ -60,7 +60,7 @@ def _create_watch_request(self, key, range_end=None, start_revision=None,
         if progress_notify:
             create_watch.progress_notify = progress_notify
         if filters is not None:
-            create_watch.filters = filters
+            create_watch.filters.extend(filters)
         if prev_kv:
             create_watch.prev_kv = prev_kv
         return etcdrpc.WatchRequest(create_request=create_watch)