debian/gbp.conf: point debian-branch to master

Git-Dch: ignore

debian/gbp.conf

@@ -2,7 +2,7 @@
 ; we need preexport here
 ;prebuild = ./prepare-release pre-export
 postbuild = ./prepare-release post-build
-debian-branch = debian/experimental
+debian-branch = master
 debian-tag = %(version)s
 export-dir = ../build-area
 sign-tags = True