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

Related: OS#3047
Change-Id: I63808c5c2724b8f4c3cf40db682f74eec54f1e76
diff --git a/contrib/jenkins.sh b/contrib/jenkins.sh
index 1dadac3..5914182 100755
--- a/contrib/jenkins.sh
+++ b/contrib/jenkins.sh
@@ -58,4 +58,5 @@
 	make -C "$base/doc/manuals" publish
 fi
 
+$MAKE maintainer-clean
 osmo-clean-workspace.sh