Destroy scrollbars without scrolling to top

[idiotWu]

As is mentioned in #66, currently scrollbar scrolls to very top when scrollbar.destroy() is called (destroy.js#L52). It would be better if native scrollbar could also stay at the same offset:

// #destroy()
container.scrollTop = this.scrollTop;
container.scrollLeft = this.scrollLeft;

Also, scrollbars should preserve the same offset when it's initialized (smooth-scrollbar.js#L28):

// #init()
const { scrollTop, scrollLeft } = container;
container.scrollTop = container.scrollLeft = 0;
this.setPosition(scrollTop, scrollLeft);