PyPy support on Focal image

Currently, the Focal image lacks PyPy and PyPy3.
They shouldn’t be hard to add.

https://travis-ci.com/github/travis-ci/cpython-builder/builds/175391765
https://travis-ci.com/github/travis-ci/cpython-builder/builds/175391984

Once they are complete, they should be available within 24 hours.

Imprint