[MRG+1] Fix FeatureAgglomeration docs

The docs are not displayed properly here, http://scikit-learn.org/stable/modules/generated/sklearn.cluster.FeatureAgglomeration.html (I keep running into these)
I should note that this hides the method in the context of `hasattr(instance, 'fit_predict')`, but does not hide it from `hasattr(cls, 'fit_predict')` nor from `dir(instance)`