code: func (a *HistogramAggregation) Order(order string, asc bool) *HistogramAggregation {
  	a.order = order
  	a.orderAsc = asc
  	return a
  }
docs: // Order specifies the sort order. Valid values for order are:
  // "_key", "_count", a sub-aggregation name, or a sub-aggregation name
  // with a metric.