Update gbp.conf for renamed branches.

debian/changelog

+osmpbf (1.3.3-13) UNRELEASED; urgency=medium
+
+  * Update gbp.conf for renamed branches.
+
+ -- Bas Couwenberg <sebastic@debian.org>  Thu, 29 Aug 2019 11:00:31 +0200
+
 osmpbf (1.3.3-12) unstable; urgency=medium
 
   * Bump Standards-Version to 4.4.0, no changes.

debian/gbp.conf

-
 [DEFAULT]
-upstream-branch = master
-debian-branch = debian
+
+# The default name for the upstream branch is "upstream".
+# Change it if the name is different (for instance, "master").
+upstream-branch = upstream
+
+# The default name for the Debian branch is "master".
+# Change it if the name is different (for instance, "debian/unstable").
+debian-branch = buster
+
+# git-import-orig uses the following names for the upstream tags.
+# Change the value if you are not using git-import-orig
+upstream-tag = upstream/%(version)s
+
+# Always use pristine-tar.
 pristine-tar = True
 
 [buildpackage]