Attempt to work around broken Mac Travis builds

Kwpolska · Kwpolska · commit d1e84a76bae7 · 2017-10-23T20:56:43.000+02:00
Signed-off-by: Chris Warrick &lt;kwpolska@gmail.com&gt;
diff --git a/.travis.yml b/.travis.yml
@@ -22,6 +22,7 @@ matrix:
     env: NMODE=nikola OS=macOS
     python: '3.6'
     before_install:
+    - brew update
     - brew install python3
     - pip3 install virtualenv
     - python3 -m virtualenv nikola-tests-venv
