databases/mysq56-{client, server}: Update to latest release 5.7.27

This update includes security fixes on issues that are
mentioned on upstream critical patch report.
Further info:
https://www.oracle.com/technetwork/security-advisory/cpujul2019-5072835.html#AppendixMSQL

PR: 239271
Submitted by: Greg Veldman <freebsd@gregv.net>
Reported by: Markus Kohlmeyer <rootservice@gmail.com>
Sponsored by: Platform.sh