Update python3 setup for brew

Author: glasnt

.travis.yml

@@ -7,7 +7,8 @@ matrix:
       os: osx
       before_install:
         - brew update
-        - brew install python3
+        - brew upgrade python
+        - pip3 install virtualenv
         - virtualenv env -p python3
         - source env/bin/activate
     - language: python