Timeline format labels funtion Date params to Moment type fix

[minsgy]

Hello, I am a user who has been finding vis-timeline very useful. I have encountered some inconveniences while using it and have decided to submit a PR.

• I would like to request a PR to modify the type of TimelineFormatLabelsFunction defined in TimelineOptions > format > minorLabels, majorLabels.
• The first date argument returned is not a Date object but a Moment object. I hope to fully utilize it by inferring the type as Moment.
• If not, it seems necessary to change the TimelineFormatLabelsFunction so that the first argument is returned as a Date. However, doing so seems like it would increase the workload, so I have opted for a simpler approach.
  Relevant images and code

Relevant images and code

// use-case
    minorLabels: (date: Date, scale: string, step: number) => {
      console.log(date)
      return ""
    },

Displayed code

�fix

• Change the first params type of the defined TimelineFormatLabelsFunction object to Moment.