BUG FIX: Use Path.relative_to() for Python 3.8 compatibility

[bswck]

.is_relative_to is 3.9+. It caused python -m devtools install to fail in Python 3.8.

https://docs.python.org/3/library/pathlib.html#pathlib.PurePath.is_relative_to

[codecov]

Codecov Report

Merging #150 (1c5362f) into main (ec406ff) will not change coverage.
The diff coverage is n/a.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #150   +/-   ##
=======================================
  Coverage   96.29%   96.29%           
=======================================
  Files           8        8           
  Lines         729      729           
  Branches      111      111           
=======================================
  Hits          702      702           
  Misses         21       21           
  Partials        6        6           

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[bswck]

I believe the CI pipeline should be configured to lint on the minimal supported Python version to ensure backward compatibility, not on 3.10 as it is configured now.
I am however hesitant to submit a patch that configures it to 3.8, since 3.7 still supported by python-devtools despite it being EOL.

[bswck]

@samuelcolvin

[samuelcolvin]

otherwise LGTM, sorry for the slow review.

[bswck]

I believe the CI pipeline should be configured to lint on the minimal supported Python version to ensure backward compatibility, not on 3.10 as it is configured now. I am however hesitant to submit a patch that configures it to 3.8, since 3.7 still supported by python-devtools despite it being EOL.

Shall I drop Python 3.7 support in a separate PR? @samuelcolvin

[samuelcolvin]

I'm happy to drop 3.7 support.

[samuelcolvin]

Thanks so much.

[bswck]

You're welcome! devtools are awesome! 🚀

[samuelcolvin]

Thanks so much.