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

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

I had pointed to some of changes not because they look wrong to me, but for the case if there are human mistakes. After your acknowledgement all LGTM.

----------
stage: patch review -> commit review

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