Issue with XGBoost + binary classification when using TreeExplainer

[imatiach-msft]

Describe the bug User reported issue. XGBoost + binary classification when using TreeExplainer fails due to bad shape.

SHAP TreeExplainer returns the wrong format for feature contribution values (lightgbm had similar issue but it was already fixed with PR https://github.com/slundberg/shap/pull/690), we have a disabled test here:

https://github.com/interpretml/interpret-community/blob/master/test/test_explain_model.py#L362

The fix requires a PR to SHAP

To Reproduce Steps to reproduce the behavior:

1. Run TreeExplainer on XGBoost binary classifier
2. See error

Expected behavior Explanation should be returned

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[imatiach-msft]

there was a workaround merged here after a user complaint: https://github.com/interpretml/interpret-community/pull/235 will keep this ticket to track the longer-term fix