In the initial implementation, we're at high risk if `scikit-learn` is updated.  We may also be at risk if `numpy` or `scipy` are updated.

I heard over and over again from folks at PyCon that this is currently the recommended way to serialize `scikit` classifiers, although everyone agrees it isn't optimal :)

Since we're keeping track of the training essays used to train the classifier, we can always retrain them after upgrading.