XGboost estimator will throw error when multiple evaluation metrics are given

[everglory99]

In xgboost scikit-learn fit API, the argument eval_metric can be a string for single metric or a list of string for multiple metrics. However, if we provide a list to the eval_metric, it will break the fit method in lore.estimators.xgboost.base. Specifically, in this and that. Can we support multiple eval metrics? I can submit a PR to fix this. Thanks!

[montanalow]

A PR would be much appreciated, including a test case that demonstrates the functionality.