[TIP] tox release 3.1.1

[toxdevorg at gmail.com]

The tox team is proud to announce the 3.1.1 bug fix release!

tox aims to automate and standardize testing in Python. It is part of
a larger vision of easing the packaging, testing and release process
of Python software.

For details about the fix(es),please check the CHANGELOG:
https://pypi.org/project/tox/3.1.1/#changelog

We thank all present and past contributors to tox. Have a look at
https://github.com/tox-dev/tox/blob/master/CONTRIBUTORS to see who
contributed.

Happy toxing,
the tox-dev team