update scroll value on scroll

[chrisdrackett]

I feel like if you are watching a scroll value you'll want to know as and when it is changing. I took a stab at adding this functionality!

closes #62

[shaulgo]

Hey, I needed the exact same behavior. I'm wondering if there's a reason not to use react's onScroll event in your pr?

Also, there's a fairly simple workaround for this. For anyone that needs this before it is merged.
You can call the measure function in the onScroll event.
<Measure client scroll onResize={({ scroll, client }) => this.onResize(scroll, client)}>
{({ measure, measureRef }) => (
<div ref={measureRef} onScroll={() => measure()}>....
)}

[souporserious]

Please use the method above using the measure function 🤗

[lxgreen]

@shaulgo it is Jun 13 2019 and I'm looking for onScroll, and find you here! 🤣