Fix division operator for Compatibility of python 3 in classifier.py

[wasnot]

On python 3, Classifier's predict () method is failed on image reshape, because using float division(/) on the reshape of the image at oversample.
On python 2, division operator / is integer division. But on python 3, / is float division and // is integer division(floored division).
And // division operator is compatible with python 2.

So, I replaced to integer division (//) which is compatible with both python 2/3.

[longjon]

This is the correct thing to do, thanks!

(Unrelatedly, at least one of our tests seems to be failing nondeterministically ಠ_ಠ)