Fix deprecation warning of setup.py check

[bagerard]

Inspired by how it got fixed in pyca/cryptography#4523
Fixes #108

[janluke]

This always gives an error after you've produced the doc in dist/docs, right?

Checking distribution dist/docs: InvalidDistribution: Unknown distribution format: 'docs'

[ionelmc]

Yeah dist/docs is a problem. I wish there was another way of doing this. Twine, an upload tool, is the wrong place to do this check.

[ionelmc]

Either way, even if twine could be the right tool the check env is not meant to build dists, and twine check would only test one of the dists - which is inadequate.

To really solve this pylibrary needs a way to automate publishing (and then piggyback twine check on top of that).

[ionelmc]

Btw it was deprecated in this ninja change: pypa/readme_renderer#122 - devoid of any discussion or explanation.

[ionelmc]

This is still on my todo list. Just need to figure out a clean way do do it cross-platform (like using some tmp dir) without mucking about in the dist folder which might have other dists there.

[Querela]

This always gives an error after you've produced the doc in dist/docs, right?

Checking distribution dist/docs: InvalidDistribution: Unknown distribution format: 'docs'

You could always specify a file extension pattern, and then it will work (with ignoring docs) ...
E.g.: twine check dist/*.{whl,gz}
I found that twine check is slightly more strict than python setup.py check [...].
But it might still check all possible distributions regardless of environment, so not sure in case of errors.