List does not update if vue-list-scroller is used inside an overflow container

[bsssshhhhhhh]

Your event mixins appear to only target the window, which breaks any cases where it is used inside an overflow container.

In this case, vue-list-scroller isn't listening to the scroll event on my overflow container, so when I scroll down the overflow container, vue-list-scroller isn't updating which items are rendered.

Check this jsfiddle (scroll down to see the problem): http://jsfiddle.net/jv6k0L37/

[IvanSafonov]

Yes, I wrote about it in README. I just don't need that feature right now and not gonna implement it any time soon. But PR's are welcome.