Update gbp.conf

Force pristine-tar, set the debian tag to collabora/xxx and disable the
user of patch numbers for gbp

Signed-off-by: Sjoerd Simons <sjoerd.simons@collabora.co.uk>

debian/gbp.conf

 [DEFAULT]
 debian-branch = collabora
+debian-tag = collabora/%(version)s
+pristine-tar = True
 
 [pq]
 patch-numbers = False