dns/powerdns: Update 4.9.7 => 4.9.8

Release notes:
https://blog.powerdns.com/powerdns-authoritative-server-4.9.8
Changelog:
https://doc.powerdns.com/authoritative/changelog/4.9.html#change-4.9.8

PR: 288812
Approved by: Ralf van der Enden <tremere@cainites.net> (maintainer)