I had to remove the scope provided in order to include the jar in the war file uploaded on appengine. Otherwise I had this following error and the instance didn't start:
```
Caused by: java.lang.ClassNotFoundException: com.google.gwt.user.client.rpc.IsSerializable
```

It seems to be linked to gae-studio but not sure. I guess that include gwt-server.jar should work as well.