MFH: r542151
databases/mysq57-{client, server}: Update to latest release 5.7.31
Full Changelog: https://dev.mysql.com/doc/relnotes/mysql/5.7/en/news-5-7-31.html
Submitted by: fluffy
Security: 0ed71663-c369-11ea-b53c-d4c9ef517024
Sponsored by: Netzkommune GmbH
Approved by: ports-secteam (with hat)