code: func NewConstantBackoff(backoffInterval, maximumJitterInterval time.Duration) Backoff {
  	return &constantBackoff{
  		backoffInterval:       int64(backoffInterval / time.Millisecond),
  		maximumJitterInterval: int64(maximumJitterInterval / time.Millisecond),
  	}
  }
docs: // NewConstantBackoff returns an instance of ConstantBackoff
  // The maximum jitter interval must be more than 1*time.Millisecond