jenkins: add missing set -e to catch build errors

Change-Id: I9f6b015b09c60c18d213dde5bbdcfc527096a10f
diff --git a/contrib/jenkins.sh b/contrib/jenkins.sh
index d9901e3..d4f98f3 100755
--- a/contrib/jenkins.sh
+++ b/contrib/jenkins.sh
@@ -1,6 +1,8 @@
 #!/usr/bin/env bash
 # jenkins build helper script for libasn1c.  This is how we build on jenkins.osmocom.org
 
+set -e
+
 set +x
 echo
 echo