try fix Python3.6 setup on Travis

Author: whtsky

ci/travis_osx_install.sh

@@ -1,6 +1,5 @@
-git clone https://github.com/MacPython/terryfy.git
-source terryfy/library_installers.sh
-clean_builds
-get_python_environment macpython $VERSION venv
+git clone https://github.com/matthew-brett/multibuild.git
+source multibuild/osx_utils.sh
+get_macpython_environment $VERSION venv
 pip install --upgrade pip wheel
 pip install -r dev-requirements.txt