Update the list of supported platforms

Update the list of supported platforms

- Change 5023 (present in BIND 9.13.3+) removed BIND's internal
  implementation of the getifaddrs() function which was required for
  iterating network interfaces on Solaris 10 as that system does not
  support that function natively.
- As of January 2019, FreeBSD 10.x is neither supported upstream nor
  regularly tested by ISC, so move it from the list of regularly tested
  platforms to the "Best effort" section.
- Debian 10, OpenBSD 6.3, and Fedora 29 have been released and are now
  tested regularly.