Update to 1.9.4

Changes: https://github.com/NLnetLabs/unbound/blob/master/doc/Changelog
PR: 241033
Reported by: C <cm@appliedprivacy.net>
Submitted by: Jaap Akkerhuis <jaap@NLnetLabs.nl> (maintainer)
Security: 108a4be3-e612-11e9-9963-5f1753e0aca0
MFH: 2019Q4