release v0.18.0
- upgrade shap to 0.39.0, which deprecated python 3.5 and added python 3.8 support
- Add cuML GPU SHAP KernelExplainer
- update abstract classes to use ABC instead of ABCMeta
- remove warning on mimic explainer relating to categorical features
- Add test case of serializing pandas timestamp
- add sparse feature importance support for lightgbm surrogate model
- add support for drop parameter in one hot encoder