Add Jython to testing matrix

[agronholm]

Since pip now works properly with Jython 2.7, Travis should be configured to test against it.

The instructions for Jython are here: https://www.topbug.net/blog/2012/05/27/use-travis-ci-with-jython/

You'll need to have it download and run the jar based installer.

[pradyunsg]

Closing as per discussion in #5121.

If there's interest in this, please feel free to send us a PR for this. :)

[lock]

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.