* Update .travis.yml
* Update .travis.yml
* updage travis.yml
* Make 3.9 support official
* Upgrade mitmproxy for Python 3.9
* Restore the Pylint job
* Undo unintended change to mitmproxy requirement
* Enable Python 3.9 in GitHub Actions
* Work around reppy’s Python version limitation
* Disable tests in Windows / Python 3.9 due to a Twisted bug
Co-authored-by: Adrián Chaves <adrian@chaves.io>