Rewrite all the Travis CI stuff to use `sudo`, because that is the only mode now (https://changelog.travis-ci.com/the-container-based-build-environment-is-fully-deprecated-84517).
Rewrite all the Travis CI stuff to use
sudo, because that is the only mode now (https://changelog.travis-ci.com/the-container-based-build-environment-is-fully-deprecated-84517).