Quote the backup contents with an * so that backups get ignored properly.

files/scripts/backup_system.sh

@@ -39,7 +39,7 @@ echo "*** Creating backup at '$BACKUP' ***"
 sudo zip -rv "$BACKUP" \
 	/etc /var/{log,mail,spool} /srv /boot \
 	/usr/local/etc $EXTRA \
-	-x /srv/backup
+	-x "/srv/backup/*"
 status="$?"
 
 if [[ "$status" != 0 ]]; then