message: Provide a better error message in the Experiment class.
diff: @@ -137,7 +137,8 @@ class Experiment(object):
  self._core_estimator_used = True
  if eval_metrics is not None:
  raise ValueError(
  - "`eval_metrics` must be `None` with `tf.estimator.Estimator`")
  + "`eval_metrics` must be `None` with `tf.estimator.Estimator`. "
  + "Use `eval_metric_ops` in `tf.estimator.EstimatorSpec` instead.")
  else:
  self._core_estimator_used = False
  if not isinstance(estimator, evaluable.Evaluable):
  