Remove Python 3.7, 2.x

[rpothier]

End support for Python 2.x, remove Python 3.7
Also merged in the changes from @doodlesbykumbi from PR #70

DEPRECATION: Python 2.7 reached the end of its life on January 1st, 2020. Please upgrade your Python as Python 2.7 is no longer maintained.
pip 21.0 will drop support for Python 2.7 in January 2021.
More details about Python 2 support in pip can be found at
https://pip.pypa.io/en/latest/development/release-process/#python-2-support

Desired Outcome

CI tests should pass.

Implemented Changes

Connected Issue/Story

Resolves #68

CyberArk internal issue link: insert issue ID

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[doodlesbykumbi]

@rpothier I saw justification for 2.7 but wondering what's the reasoning behind removing 3.7 ?