Pass on **kwargs in plot_shap_values of base meta leaner

[kklein]

Proposed changes

As of now, the plot_shap_values method of the base meta learner class has a **kwargs parameter. Yet, the latter isn't actually passed to the plot_shap_values method of the explainer. The latter would pass those to actual plotting methods, allowing e.g. for setting show=False.

Types of changes

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Checklist

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Further comments

This is analogous to #603.

[kklein]

Hi @jeongyoonlee, is there something I would need to provide to make this PR move forward?

[jeongyoonlee]

Builds are failing due to the change in the latest numpy and pandas. I submitted #631 to fix it. Once we confirm all builds pass, we can approve and merge this PR.

[jeongyoonlee]

LGTM