code: func (c *Client) PutFormation(formation *ct.Formation) error {
  	if formation.AppID == "" || formation.ReleaseID == "" {
  		return errors.New("controller: missing app id and/or release id")
  	}
  	return c.Put(fmt.Sprintf("/apps/%s/formations/%s", formation.AppID, formation.ReleaseID), formation, formation)
  }
docs: // PutFormation updates an existing formation.