[docs] [issue30312] Small correction in set code sample

[Mariatta Wijaya]

Mariatta Wijaya added the comment:

Documentation has been updated, and backported to 3.6.
Thanks :)

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resolution:  -> fixed
stage: backport needed -> resolved
status: open -> closed

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue30312>
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