GradientBoostingRegressor mentions the non-existing early_stopping parameter, while GradientBoostingClassifier does not. The doc-strings should probably be synced.
http://scikit-learn.org/dev/modules/generated/sklearn.ensemble.GradientBoostingRegressor.html#sklearn.ensemble.GradientBoostingRegressor