Fix homebrew path.

Author: jdm

.travis.yml

@@ -35,7 +35,7 @@ env:
 
 before_script:
   - if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then export CC=gcc-6; export CXX=g++-6; fi
-  - if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then export PYTHON3="/usr/local/opt/python3/bin/python3"; fi
+  - if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then export PYTHON3="/usr/local/opt/python/bin/python3"; fi
 
 script:
   - ccache -z