Remove os.getenv("JUPYTERHUB_USER") from [this line](https://github.com/DigiKlausur/e2xgrader/blob/3a1ba76a1a4939848203bc0b68967ee4d0105d45/e2xgrader/exchange/fetch_assignment.py#L72) because `src` already contains a complete personalized outbound path
