Add GIMP's "po-windows-installer" to hooks.po-directories

[Rafael Fontenelle <rafaelff gnome org>]

Sysadmins,

Can you please include GIMP's "po-windows-installer" dir to
"hooks.po-directories" ?

I'm trying to send translation to repository via Damned Lies, but I'm
getting the following error message:

“[Errno 1] b"remote: translations user cannot modify
'po-windows-installer/pt_BR.po' \nTo ssh://git.gnome.org/git/gimp\n !
[remote rejected] master -> master (pre-receive hook declined)\nerror:
failed to push some refs to 'ssh://git.gnome.org/git/gimp'\n"”

I assume it happens because this directory "po-windows-installer" a
non-standard directory and not present in hooks.po-directories,
therefore denied by default.
(https://git.gnome.org/browse/sysadmin-bin/tree/git/pre-receive-check-translations)

Thanks in advance,
Rafael Fontenelle