[issue4648] Fix n//x to n/x in the Docs

[Retro]

Retro <vinetouu at gmail.com> added the comment:

For Python 2.x that example code is fine, but Python 3.0 has this
switched now. Please read http://www.python.org/dev/peps/pep-0238/.

True division in Python 3.0 is done with one division operator. Please
fix that code example to reflect that.

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