Check if self.estimator has 'method'.

        Raises
        ------
        AttributeError

def _check_method(self, method):
        """Check if self.estimator has 'method'.

        Raises
        ------
        AttributeError
        """
        estimator = self._postfit_estimator
        if not hasattr(estimator, method):
            msg = "The wrapped estimator '{}' does not have a '{}' method.".format(
                estimator, method
            )
            raise AttributeError(msg)
        return getattr(estimator, method)