Update tox to 4.21.2#576

pyup-bot wants to merge 1 commit intomastermatt2000/json_stream_reader:masterfrom

pyup-update-tox-3.8.6-to-4.21.2matt2000/json_stream_reader:pyup-update-tox-3.8.6-to-4.21.2Copy head branch name to clipboard