drop python2 from CI

[dulmandakh]

The issue

PIP dropped Python 2 support pypa/pip#6148, therefore pipenv needs to drop Python 2 and make performance improvements.

I would like to volunteer sometime to drop Python 2.

The fix

Let's drop Python 2 from CI, then we can do other cleanups safely.

The checklist

• Associated issue
• A news fragment in the news/ directory to describe this fix with the extension .bugfix, .feature, .behavior, .doc. .vendor. or .trivial (this will appear in the release changelog). Use semantic line breaks and name the file after the issue number or the PR #.

[frostming]

Thanks for that, to drop Python 2 there are some more to do:

• Remove six and other backport libraries
• Modernize the codebase to Py3.6+
• Remove compatible codes

I will merge this shortly

[dulmandakh]

@frostming I would like to work on removing six once this merged. Thanks