security/vuxml: also list mailman exim4/postfix pkgs

The initial commit 162e701a5982 omitted listing the
-exim4 and -postfix packages. Make up for that.

Security: 9d7a2b54-4468-11ec-8532-0d24c37c72c8
Security: CVE-2021-43331
Security: CVE-2021-43332