Message 320762 - Python tracker

As noted in https://github.com/travis-ci/travis-ci/issues/9069, Travis CI's Ubuntu 14.04 environment includes an OpenSSL that's too old to meet Python 3.7's security requirements.

According to https://github.com/travis-ci/travis-ci/issues/9069#issuecomment-395471575, setting "dist: xenial" instead (giving Ubuntu 16.04) provides a testing environment with a new enough OpenSSL for 3.7 to work.

I'm thinking it would make the most sense as a subsection under https://docs.python.org/dev/whatsnew/3.7.html#platform-support-removals

(https://docs.python.org/dev/whatsnew/3.7.html#ssl does mention this information in a note, but that uses the OpenSSL version numbers directly, which folks aren't necessarily going to know to go to distrowatch to check which Travis environment they need to select: https://distrowatch.com/table.php?distribution=Ubuntu )