Update gpo.py

[github at samba.org]

New comment by douglasbagnall on Samba Github repository

https://github.com/samba-team/samba/pull/123#issuecomment-448826562
Comment:
@lausser: Sorry we have left this so long. We are abandoning Github for Gitlab.

Thanks. This looks like an obvious improvement. Could you

1. add this to the commit message:
```
Signed-off-by: Gerhard Lausser <gerhard.lausser at consol.de>
```
2. ideally assert you have personal copyright or follow the DCO steps here https://www.samba.org/samba/devel/copyright-policy.html

and for extra points:

3. either raise on https://gitlab.com/samba-team/samba/ or send to the mailing list (subscribe via https://lists.samba.org/mailman/listinfo/samba-technical)

I realise this is a lot of fussing around for such a small patch. Sorry and thanks again.