Update tox.ini
Update tox.ini

- add `[flake8]` configuration section (see #2995)
- remove CLI test list from `[testenv:flake8]` section (will use `[flake8]` config
- remove 'Lib' folder from `[testenv:flake8]` section (will now check all .py files)

googlefonts/fontbakery,googlefonts/fontbakery,moyogo/fontbakery,graphicore/fontbakery,googlefonts/fontbakery,moyogo/fontbakery,graphicore/fontbakery,moyogo/fontbakery,graphicore/fontbakery