Fix for #25 (and afterAnimate)

[xehpuk]

animateScroll previously returned immediately which resulted in updateHistory and afterAnimate to run before the animation. It nor returns a Promise which is resolved when the animation ends and is rejected if there isn't an element with the given ID.
This previously was a warning emitted by fbjs (and its last usage). So now it's kicked out of the readme.

The package-lock.json should be committed into source repositories.

[bySabi]

@xehpuk your commit are absolutely great.
Make animateScroll async was a good catch, I forget the non-blocking nature of setTimeout

Only one thing. Could you reimplement animateScroll with async/await? . I thing this will make the code more readable. If you have the time, of course :-)

[xehpuk]

Phew, not sure how to do it or if it's even possible without using a Promise for the "callback nature" of setTimeout. Maybe you have an idea?

[bySabi]

At the end, the solution, promisify setTimeout, looks more tricky.

Thanks for take your time on this.