test(docker_compose): adjust ssl to be certs DIR

The directory was renamed from '/ssl' to '/certs'

MR !2

test/docker-compose.yml

@@ -86,7 +86,7 @@ services:
     hostname: mail.nofusscomputing.com
     volumes:
       - mail_store:/srv/mail:rw
-      - mail_ssl:/ssl
+      - mail_ssl:/certs
       - sa_learn:/var/spool/spamassassin
       - mail_backup:/backup
       - mail_log:/var/log