Fixed MqttServiceClient unsubscribe not unpacking the tuple returned from the underlying mqtt_connection method (#38)

Co-authored-by: Josh Wells <[email protected]>

Author: zakini

awsiot/__init__.py

@@ -58,7 +58,7 @@ def on_unsuback(unsuback_future):
                 else:
                     future.set_result(None)
 
-            unsub_future = self.mqtt_connection.unsubscribe(topic)
+            unsub_future, _ = self.mqtt_connection.unsubscribe(topic)
             unsub_future.add_done_callback(on_unsuback)
 
         except Exception as e: