avoid importing detect_secrets in setup.py

[bo5o]

Fixes #407

[domanchi]

🤦 Thanks for this, @cbows!

[michael-anselmi]

This should accommodate platforms that don't use / as a path separator:

Suggested change

	versionpy = Path('detect_secrets/__version__.py').read_text()
	versionpy = Path('detect_secrets').joinpath('__version__.py').read_text()

[domanchi]

Fair point. Will ensure this gets added to the patch version.

[bo5o]

not sure if pathlib handles this by default anyway, but a more pythonic way would be to write Path('detect_secrets') / '__version__.py'. / is actually overloaded for path objects to do the right thing.

EDIT: I just checked using '/' in Windows, and it just works. This is also documented behavior (see https://docs.python.org/3/library/pathlib.html#pathlib.PurePath)