code: func NormalDistribution(generator *rand.Rand, standardDeviation float64) Transformation {
  	random := fallbackNewRandom(generator)
  
  	return func(duration time.Duration) time.Duration {
  		return time.Duration(random.NormFloat64()*standardDeviation + float64(duration))
  	}
  }
docs: // NormalDistribution creates a Transformation that transforms a duration into a
  // result duration based on a normal distribution of the input and the given
  // standard deviation.
  //
  // The given generator is what is used to determine the random transformation.
  // If a nil generator is passed, a default one will be provided.