Update mail/postfixadmin to 3.0.2 (security fix)

SECURITY FIX: don't allow to delete protected aliases
(CVE-2017-5930, PR#23).

Following non-security bugs were fixed:

• Fix VacationHandler for PostgreSQL
• AliasHandler: restrict mailbox subquery to allowed and specified domains to improve performance on setups with

+lots of mailboxes

• Allow switching between dovecot: password schemes while still accepting passwords hashed using the previous dov

+ecot: scheme

• FetchmailHandler: use a valid date as default for 'date'
• Fix date formatting in non-english languages when using PostgreSQL

PR: 216932
Submitted by: lukasz@wasikowski.net
Approved by: maintainer, mat (mentor)
Differential Revision: https://reviews.freebsd.org/D9521