Work around slop in Travis OSX support

Author: kislyuk

.travis.yml

@@ -23,8 +23,7 @@ matrix:
     - python: pypy3
 
 install:
-  - if [[ $TRAVIS_OS_NAME == osx ]]; then brew update; fi
-  - if [[ $TRAVIS_OS_NAME == osx ]]; then brew install openssl python$PYTHON_VERSION; fi
+  - if [[ $TRAVIS_OS_NAME == osx ]] && [[ $PYTHON_VERSION == 3 ]]; then brew upgrade python; pip3 install --ignore-installed virtualenv; fi
   - if [[ $TRAVIS_OS_NAME == osx ]]; then export LDFLAGS="-L$(brew --prefix openssl)/lib" CFLAGS="-I$(brew --prefix openssl)/include"; fi
   - virtualenv --python=python$PYTHON_VERSION env
   - source env/bin/activate