Swarm Mode service scaling parameter mistake is fixed.

Signed-off-by: Güray Yıldırım <guray@gurayyildirim.com.tr>

docker/models/services.py

@@ -126,7 +126,7 @@ class Service(Model):
 
         service_mode = ServiceMode('replicated', replicas)
         return self.client.api.update_service(self.id, self.version,
-                                              service_mode,
+                                              mode=service_mode,
                                               fetch_current_spec=True)
 
     def force_update(self):