.travis.yml: Revert to using autoblack (#2033)

* .travis.yml: Revert to using autoblack

Our autoblack GitHub Action will get us to black compliance without forcing each contributor to learn about, install, and use psf/black on every pull request.

* updating DIRECTORY.md

Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>