Placement Is Off when :class is used on a child container

[justwiebe]

Repro link: https://codesandbox.io/s/vue-smooth-dnd-nested-bug-thwo5e

When :class is used in a nested dnd container, Vue removes the smooth-dnd-container class from the element and it's never put back on. This causes smooth-dnd to use the parent container as a reference for where to place the dropped element in the list.

Workaround: use a wrapper or child div to put the class on instead of putting it on the <container>