minor update to crontab

src/mailsrv/assets/crontab

@@ -1,4 +1,4 @@
 # m h  dom mon dow   command
 
 # Do daily mail maintenance
-11 1   *   *   *     /bin/bash -c 'for f in /vol/data/cron.d/*; do $f; done'
+11 1   *   *   *     /bin/bash -c 'for f in /vol/data/cron.d/*.sh; do $f; done'