Drop support for ruby < 2.5
Drop support for ruby < 2.5

Future versions of the library may work with these versions, but will
not be maintained as such. 2.4 and earlier are not officially supported,
so this is an encouragement to move to versions that are:
https://www.ruby-lang.org/en/news/2020/04/05/support-of-ruby-2-4-has-ended/

Empact/roxml,Empact/roxml