Safari support

[LuisReinoso]

Hi, I really love this software ;) But I note that this is not working on Safari Browser. Because active class is not setting on the DOM.

Could you give some advice that from where I should have to start to support this browser.

I have tried:

• install polyfills intersection-observer has you tell in readme.
• to check if it works I use https://github.com/w3c/IntersectionObserver/issues/296#issuecomment-384979453 but this return false also safari doesn't works
• and this one too. https://github.com/w3c/IntersectionObserver/issues/282

I try to make it work on safari < 12.1. That doesn't have official support.

Thanks!