Update minimum Ruby to 3.1

[SalvatoreT]

Update the dependencies to the latest versions.

Ruby 3.2 dropped support for File.exists? and only has the singular File.exist?.

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📝 Checklist

• Commit messages provide context (why not just what, some tips here).
• If relevant, mention GitHub issue number above and include in a commit message.
• Latest code from master merged.
• New behaviour has test coverage.
• Avoid duplicating code.
• No commented out code.
• Avoid comments for your code, write code that explains itself.
• Changes are simple, useful, clear and brief.

[matthutchinson]

✅ Thanks for this, looks great, will merge and prep a new release shortly

[matthutchinson]

Sorry for the huge delay, I'm now working on some cleanups to this gem, to bring it into the modern Ruby age, this PR is a great first step! 🙇‍♂️

[SalvatoreT]

Yay! I love this tool so much.