contrib/jenkins.sh: run "make maintainer-clean"

Related: OS#3047
Change-Id: Ifc91733c7fe0c5a002037523116014bf270997ef
diff --git a/contrib/jenkins.sh b/contrib/jenkins.sh
index be8dadc..dca33bb 100755
--- a/contrib/jenkins.sh
+++ b/contrib/jenkins.sh
@@ -78,4 +78,5 @@
 	make -C "$base/doc/manuals" publish
 fi
 
+$MAKE maintainer-clean
 osmo-clean-workspace.sh