code: func (a *ACL) Update(acl *ACLEntry, q *WriteOptions) (*WriteMeta, error) {
  	r := a.c.newRequest("PUT", "/v1/acl/update")
  	r.setWriteOptions(q)
  	r.obj = acl
  	rtt, resp, err := requireOK(a.c.doRequest(r))
  	if err != nil {
  		return nil, err
  	}
  	defer resp.Body.Close()
  
  	wm := &WriteMeta{RequestTime: rtt}
  	return wm, nil
  }
docs: // Update is used to update the rules of an existing token
  //
  // Deprecated: Use TokenUpdate instead.