code: func (b *ProgressBar) Step() int {
  	b.mtx.Lock()
  	defer b.mtx.Unlock()
  	b.value++
  
  	if b.value > b.max {
  		b.value = b.max
  	}
  
  	return b.value
  }
docs: // Step increases ProgressBar value by 1 if the value is less
  // than ProgressBar high limit