[docs] [issue16077] fix code example in docs for built-in reduce()

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

I thought and decided it wasn't worth it. Howtos for general cases, and not for corner cases.

----------

_______________________________________
Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue16077>
_______________________________________