async changePermissionGroup (id, name, rule) {
    const result = await db('permission_groups').where('id', id).update({
      name,
      rule: JSON.stringify(rule),
      updateTime: (new Date()).getTime()
    })

    return result
  }
Change permisssion group

@param {Int} gid group id
@param {String} name group name
@param {Object} rule group rule

@returns {Int}