We should update the gemspec, tests, and anywhere else that uses Ruby 2.3 and 2.4 and settle on Ruby 2.5 as the minimum supported version (since that's what Puppet 6 uses).
We should bump the Y version in Facter when we complete this.
Wondering if we should drop Ruby 2.5 as well? One reason against that is it would break "puppet facts diff" command in 6.x. We could probably drop Ruby 2.5 in facter later on after 6 is officially EOL.