[docs] [issue20464] Update distutils sample config file in Doc/install/index.rst

[Zachary Ware]

Change by Zachary Ware <zachary.ware at gmail.com>:


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versions: +Python 3.7 -Python 3.4, Python 3.5

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue20464>
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