Fix commands_pre/commands_post documentation.

[benoit-pierre]

Mention the minimum version required.

[gaborbernat]

The linting fails 😢

[benoit-pierre]

Should be fixed.

[gaborbernat]

Thanks!

[cjerdonek]

Has there been any consideration of having tox issue a warning if unrecognized key values are encountered? That could help people to know they could need to upgrade. Currently, such key values (e.g. commands_pre) are silently skipped if the user doesn't have a new enough version.

[gaborbernat]

No, and probably we'll never have it. This would be backwards incompatible change. Note people can at the moment use empty keywords together with substitution to re-use fields, e.g.:

[testenv]
doc_python = python3

[testenv:doc_build]
basepython = {[testenv]doc_python}

[testenv:doc_build2]
basepython = {[testenv]doc_python}

If you depend on a feature that's only available under a given version you should specify it via the minversion https://tox.readthedocs.io/en/latest/config.html#conf-minversion

tox configuration specification — tox 3.5.2.dev17 documentation