Add Polyfill intersection-observer

[ridhoassuryadi]

Hi I have a problem when using this library when on a Safari Browser. Namely the problem of the absence of fire observer-intersections on safari. can you add it to this library?

[jengel3]

I think it would be better to handle adding the polyfill yourself - however I do think that the library should automatically detect if the browser supports IntersectionObserver or not because otherwise it will throw errors, especially when observer.disconnect() is called here

[alexjoverm]

Yes, it's better to handle the polyfill yourself. It wouldn't be a bad idea to have some checks in the library for sure.

[alexjoverm]

From 1.3.1, it will check for IntersectionObserver and throw an Error if it doesn't find it 🎉