Update tox to 3.21.2#213

pyup-bot wants to merge 1 commit intomasterwdar/cdippy_2018:masterfrom

pyup-update-tox-3.5.2-to-3.21.2wdar/cdippy_2018:pyup-update-tox-3.5.2-to-3.21.2Copy head branch name to clipboard