fix: keyField issue for class instances, fix #770 (#771)

Author: shreymahendru

packages/vue-virtual-scroller/src/components/DynamicScrollerItem.vue

@@ -58,7 +58,7 @@ export default {
     id () {
       if (this.vscrollData.simpleArray) return this.index
       // eslint-disable-next-line no-prototype-builtins
-      if (this.item.hasOwnProperty(this.vscrollData.keyField)) return this.item[this.vscrollData.keyField]
+      if (this.vscrollData.keyField in this.item) return this.item[this.vscrollData.keyField]
       throw new Error(`keyField '${this.vscrollData.keyField}' not found in your item. You should set a valid keyField prop on your Scroller`)
     },