[issue13086] Update howto/cporting.rst so it talks about 3.x instead of 3.0

[Ezio Melotti]

Changes by Ezio Melotti <ezio.melotti at gmail.com>:


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nosy: +ezio.melotti
stage:  -> needs patch
versions:  -Python 3.1, Python 3.4

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<http://bugs.python.org/issue13086>
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