use production branch if overlay.xml is checked out from there

@@ -10,7 +10,7 @@
 		<owner>
 			<email>georg@steffers.org</email>
 		</owner>
-		<source type="git">
+		<source type="git" branch="production">
 			https://gitlab.weird-web-workers.org/ghopp/ghopp-overlay.git
 		</source>
 	</repo>