[docs] [issue25523] Correct "a" article to "an" article

[Roundup Robot]

Roundup Robot added the comment:

New changeset 651f7addf4a8 by Martin Panter in branch '2.7':
Issue #25523: Correct "a" article to "an" article
https://hg.python.org/cpython/rev/651f7addf4a8

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue25523>
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