PyPy 2.7 on Xenial

Environments Xenial
4

PyPy2.7-6.0 and PyPy3.5-6.0 should both be available on Xenial.

https://travis-ci.org/BanzaiMan/travis_production_test/jobs/463979910#L449-L451
https://travis-ci.org/BanzaiMan/travis_production_test/jobs/463979911#L449-L451