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

Related: OS#3047
Change-Id: I733df8f8bfaf448a6507c9c9d75d2f076fedb342
diff --git a/contrib/jenkins.sh b/contrib/jenkins.sh
index e805080..8c32cbb 100755
--- a/contrib/jenkins.sh
+++ b/contrib/jenkins.sh
@@ -104,4 +104,5 @@
   make -C "$base/doc/manuals" publish
 fi
 
+$MAKE maintainer-clean
 osmo-clean-workspace.sh