setup: Only require configparser when native version unavailable

[jtojnar]

On Python 3, configparser library is part of standard library. The configparser package therefore is not needed. For this reason, distributions such as Arch Linux do not even provide this package for Python 3, which in turn breaks the build.

This patch changes the setup.py to only add the configparser dependency when native configparser is not available.

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Codecov Report

Merging #232 into develop will not change coverage. The diff coverage is n/a.

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  Hits           899      899           
  Misses          13       13           
  Partials        22       22

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[jtojnar]

Apparently, it is possible to declare version-specific constraints: https://github.com/joke2k/faker/blob/f81cd517e35d72edbdb264d0ec6a0f93f8d37ab8/setup.py#L68-L78