code: func (cli *Client) NodeUpdate(ctx context.Context, nodeID string, version swarm.Version, node swarm.NodeSpec) error {
  	query := url.Values{}
  	query.Set("version", strconv.FormatUint(version.Index, 10))
  	resp, err := cli.post(ctx, "/nodes/"+nodeID+"/update", query, node, nil)
  	ensureReaderClosed(resp)
  	return err
  }
docs: // NodeUpdate updates a Node.