Our Python 2.7.12 tests can't run

[nworden]

Our tests for Python 2.7.12 now fail with this error:
Unable to download 2.7.12 archive. The archive may not exist. Please consider a different version.
I'd really like to consider a different version, but unfortunately, as far as I can tell, App Engine's Python 2 runtime still uses 2.7.12 (the last Python runtime update in the release notes was the May 2017 update to 2.7.12).
I'll try fiddling with our Travis config to see if there's another way to run these. It's not a huge deal since we're on our way to Python 3 anyway, but we have a had an issue in the past (#575) that depended on the micro version we were running.