Xgboost warning

when running example script with Titanic data, I got warning:
```
/xgboost/training.py:38: UserWarning: `feval` is deprecated, use `custom_metric` instead.  They have different behavior when custom objective is also used.See https://xgboost.readthedocs.io/en/latest/tutorials/custom_metric_obj.html for details on the `custom_metric`.
```