code: func NewRetryTransport(retrier *retry.Retrier, transport RoundTripper) *RetryTransport {
  	return &RetryTransport{
  		Retrier: retrier,
  		MethodsToRetry: map[string]bool{
  			"":     true, // http.Client treats empty methods the same as "GET"
  			"GET":  true,
  			"HEAD": true,
  		},
  		Transport: transport,
  	}
  }
docs: // NewRetryTransport returns a RetryTransport that will retry idempotent HTTP
  // requests (GET/HEAD) using the given retrier.