[BUG] Placeholder shifted after scroll of container

[ivictbor]

1. Cloned repo version": "0.8.1"

2. Added style='max-height: 400px; overflow-y: auto' to container

/vue-smooth-dnd (master) $ git diff
diff --git a/demo/src/pages/cards.vue b/demo/src/pages/cards.vue
index 863e41c..40f91d1 100644
--- a/demo/src/pages/cards.vue
+++ b/demo/src/pages/cards.vue
@@ -14,6 +14,7 @@
             {{ column.name }}
           </div>
           <Container
+            style='max-height: 400px; overflow-y: auto'
             group-name="col"
             @drop="(e) => onCardDrop(column.id, e)"
             @drag-start="(e) => log('drag start', e)"

3. npm run dev

4. Scroll 2nd stage and start moving first card

Video with same instructions: https://screencast-o-matic.com/watch/cqli6TULp5