Fix macOS Python 2.6 builds on Travis CI (#614)
Fix macOS Python 2.6 builds on Travis CI (#614)

Summary:
get-pip.py dropped support for Python 2.6. This causes our CI scripts
which set up Python 2.6 on macOS to fail.

pyenv has a workaround: when installing Python 2.6, use a version of
get-pip.py which is compatible with Python 2.6. This workaround requires
a recent version of pyenv. Unfortunately, `brew install pyenv` refuses
to upgrade pyenv.

Install the latest version of pyenv by running `brew upgrade pyenv`
instead of `brew install pyenv`. This causes pyenv to use a working
version of get-pip.py, fixing the setup of Python 2.6.
Closes https://github.com/facebook/watchman/pull/614

Reviewed By: wez

Differential Revision: D8320979

Pulled By: strager

fbshipit-source-id: fcdfa3555122ceacd2bf73582a588ae073e9a7f9

facebook/watchman,nodakai/watchman,nodakai/watchman,facebook/watchman,facebook/watchman,facebook/watchman,nodakai/watchman,wez/watchman,wez/watchman,nodakai/watchman,wez/watchman,nodakai/watchman,nodakai/watchman,facebook/watchman,nodakai/watchman,facebook/watchman,wez/watchman,wez/watchman,wez/watchman,wez/watchman,wez/watchman,wez/watchman,nodakai/watchman,facebook/watchman,facebook/watchman,nodakai/watchman,facebook/watchman