tweak Vimeo duration logic

[ghost]

Hey!
It's about that issue: #250
If we want to add setDuration logic in this.player.ready().then(...) instead of this.player.on("loaded"), we also should to add the tweak from that PR.

[cookpete]

Good spot. Maybe we should move it to loaded event listener instead so we don't have to repeat?

this.player.on('loaded', () => {
  this.onReady()
  this.player.getDuration().then(duration => {
    this.duration = duration
  })
})

[ghost]

@cookpete #250 (comment) :)
Can I do it?