Fix scrollend event not being fired in some cases

In certain cases the "scrollend" event is never fired. Chrome and Firefox rounds values down for scrollTop and scrollHeight.

In some cases contentScrollTop is one less than maxScroll top despite being scrolled all the way down.

```
  if @contentScrollTop >= @maxScrollTop and @prevScrollTop isnt @maxScrollTop
            @$el.trigger 'scrollend'
```