code: func (actor Actor) SetOrganizationDefaultIsolationSegment(orgGUID string, isoSegGUID string) (Warnings, error) {
  	_, apiWarnings, err := actor.CloudControllerClient.UpdateOrganizationDefaultIsolationSegmentRelationship(orgGUID, isoSegGUID)
  	return Warnings(apiWarnings), err
  }
docs: // SetOrganizationDefaultIsolationSegment sets a default isolation segment on
  // an organization.