[docs] [issue25212] Remove the double spaces in the C-API Intro

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

PEP 8: You should use two spaces after a sentence-ending period.

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nosy: +serhiy.storchaka

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue25212>
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