code: func NewLinear(cfg LinearConfig) (*Linear, error) {
  	if err := cfg.CheckAndSetDefaults(); err != nil {
  		return nil, trace.Wrap(err)
  	}
  	closedChan := make(chan time.Time)
  	close(closedChan)
  	return &Linear{LinearConfig: cfg, closedChan: closedChan}, nil
  }
docs: // NewLinear returns a new instance of linear retry