Python 2.6 failed to setup in CI test

[davidlatwe]

Problem

In the time I made PR #184 , Python 2.6 start failing to pass the CI test setup, due to pytest-runner not able to find the package setuptools_scm. Checkout branch master to build test also showed same result.

Discussion

Based on this fact, can Python 2.6 be dropped ?

[msiemens]

I think this should be fine as pip also dropped support for Python 2.6 (see pypa/pip#3955). If no one else has any objections, we can do this.

@eugene-eeo

[hugovk]

Please see PR #188.