Class drag-over isn't removed once added

[tijptjik]

Tested in Chrome and Firefox -- the drag-over class is added, but not removed correctly

E.g. on your demo page, all items add up with the drag-over styling:

[legowhales]

I was about to create the same issue 😉

[Spikeysanju]

@Bxnq Thanks for the PR. It's live. I've refactored the demo.

Custom.classes.SvelteDND.mp4