Add 18.04 Bionic, remove EOL 14.04 Trusty

[hugovk]

• Add Ubuntu 18.04 (Bionic Beaver)

• Add version number to Trusty and Xenial to retain chronological listings

• Upgrade pip to fix Trusty: a dependency (More Itertools) has just dropped support for Python 2. Modern pip installs the right version because More Itertools added python_requires, so upgrade from ancient 2014 pip. (This has started failing in master.)

  • Might as well always upgrade pip in all containers

[radarhere]

You may still wish to update pip anyway, but seeing that a later master build for the same commit passed, I rerun the failing job from the Travis build that you linked to, and it passes now.

[hugovk]

Ah yes, Pytest added a workaround (pytest-dev/pytest#4774) to prevent it for ancient pip.

Thanks for the note! I still think it's a good idea to use modern pip to make sure things install consistently.

[hugovk]

Updated to drop EOL Ubuntu 14.04 (Trusty Tahr).

• https://linuxlifecycle.com/