`SortableItem.className` is discarded

[gera2ld]

SortableItem.className is discarded, is that accidental or in purpose?

As a result, code below does not work:

<SortableContainer className="hello">
  <div />
</SortableContainer>

// this does not work either
<SortableContainer>
  <div className="hello" />
</SortableContainer>

Ref:

react-anything-sortable/src/SortableItemMixin.js

Line 99 in 4d7dbe6

render() {