Tolerate more Python versions in link overwrite

.travis.yml

@@ -34,7 +34,7 @@ before_install:
   # inability to link it as an error and fail the command. You can --force a link step, but
   # I don't see a way to tell it to not replace things that exist and also not fail.
   - if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then brew bundle --verbose || true; fi
-  - if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then brew link --overwrite python@3.8; fi
+  - if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then brew link --overwrite python@3.9 || brew link --overwrite python@3.8 || true; fi
   # Try installing gcc6 twice in case of errors like this:
   # Error: HOMEBREW_LOGS was not exported!
   # Please don't worry, you likely hit a bug auto-updating from an old version.