Update README with latest gem version

[oneroyalace]

Version 4.5.0, which is referenced in the README, doesn't work with new versions of ActiveSupport:

Bundler could not find compatible versions for gem "activesupport":
  In snapshot (Gemfile.lock):
    activesupport (= 7.0.2.4)

  In Gemfile:
    comma (~> 4.5.0) was resolved to 4.5.0, which depends on
      activesupport (< 6.2, >= 4.2.0)

    rails (~> 7.0.2.3) was resolved to 7.0.2.4, which depends on
      activesupport (= 7.0.2.4)

Running `bundle update` will rebuild your snapshot from scratch, using only
the gems in your Gemfile, which may resolve the conflict.

[eitoball]

Thank you.