Bump up ruby requirement?

[jjb]

This PR #159 fails on an older version of ruby

Maybe support for older rubies could be dropped.

• idea 1: require 3.2 or later (3.1 and older are unsupported https://www.ruby-lang.org/en/downloads/branches/ )
• idea 2: require 3.0 or later (likelyhood of api/behavior requirements starting there)