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

Related: OS#3047
Change-Id: Ic887518bd149f325a92c3517ee90c655b1368fd8
diff --git a/contrib/jenkins.sh b/contrib/jenkins.sh
index a9d871f..51583f8 100755
--- a/contrib/jenkins.sh
+++ b/contrib/jenkins.sh
@@ -77,4 +77,5 @@
 	make -C "$base/doc/manuals" publish
 fi
 
+$MAKE maintainer-clean
 osmo-clean-workspace.sh