spinner does not update according to its phases if there are too few state modification

[mandelsoft]

The spinner only updates its rendered state, if the content of the bar is changed. If this happens not often enough the spinner character is not updated.

For example:

`       bar := progressbar.NewOptions(-1, progressbar.OptionSetDescription("test"), progressbar.OptionSpinnerType(15))
    for i := 0; i < 10; i++ {
        bar.Describe(fmt.Sprintf("test"))
        time.Sleep(1000 * time.Millisecond)
    }

It should iterate all letters, but it only shows a new letter if a Describe is called. As a result the spinner effect is gone.

[schollz]

pr welcome