Link to IntersectionObserver in readme is broken

From the readme:

> Yet another Lazy Loading JavaScript library, why?
> Existing lazy loading libraries hook up to the scroll event or use a periodic timer and call getBoundingClientRect() on elements that need to be lazy loaded. This approach, however, is painfully slow as each call to getBoundingClientRect() forces the browser to re-layout the entire page and will introduce considerable jank to your website.
>
> Making this more efficient and performant is what [IntersectionObserver](https://developers.google.com/web/updates/2016/04/intersectionobserver) is designed for, and it’s landed in Chrome 51. IntersectionObservers let you know when an observed element enters or exits the browser’s viewport.

Broken link: [IntersectionObserver](https://developers.google.com/web/updates/2016/04/intersectionobserver)