dns/knot-resolver: update 5.0.1 -> 5.1.1

PR: 246578
Approved by: freebsd@dns.company (maintainer timeout)
Relnotes: https://www.knot-resolver.cz/2020-05-19-knot-resolver-5.1.1.html
Security: CVE-2020-12667
MFH: 2020Q2