Backport PR #17862: CI: Install, or upgrade, Python 3 on homebrew.

tacaswell · meeseeksmachine · commit 721f4f722042 · 2020-07-08T23:52:06.000Z
diff --git a/.travis.yml b/.travis.yml
@@ -115,7 +115,7 @@ before_install: |
     ci/silence brew update
     brew uninstall numpy gdal postgis
     brew unlink python@2
-    brew upgrade python
+    brew install python || brew upgrade python
     brew install ffmpeg imagemagick mplayer ccache
     hash -r
     which python
