[docs] [issue28960] Small typo in Thread.join docs

[beautifuljose]

beautifuljose <terryjosephinee at gmail.com> added the comment:

I think both dash and comma should be removed
Found a similar problem here: 
https://www.paperhelp.org/essay/buy-argumentative-essay.html

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nosy: +beautifuljose

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue28960>
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