Log Message:
math/py-scikit-learn: Update to 0.22.1

Highlights:

- New plotting API
- Stacking Classifier and Regressor
- Permutation-based feature importance
- Native support for missing values for gradient boosting
- Precomputed sparse nearest neighbors graph
- KNN Based Imputation
- Tree pruning
- Retrieve dataframes from OpenML
- Checking scikit-learn compatibility of an estimator
- ROC AUC now supports multiclass classification