Fixed a typo in the Python 3 compatibility docs.

six_ is the canonical compatibility library for supporting Python 2 and 3 in

a single codebase. Read its documentation!

:mod`six` is bundled with Django as of version 1.4.2. You can import it as

:mod`django.utils.six`.

:mod:`six` is bundled with Django as of version 1.4.2. You can import it as

:mod:`django.utils.six`.

Here are the most common changes required to write compatible code.