Validate the quantiles passed in. Returns the np array if valid.

def _check_quantiles(self, val):
        """
        Validate the quantiles passed in. Returns the np array if valid.
        """
        if len(val) != 3 or not is_monotonic(val) or not np.all(val < 1):
            raise YellowbrickValueError(
                "quantiles must be a sequence of three "
                "monotonically increasing values less than 1"
            )
        return np.asarray(val)