Fix compile errors

Author: zetashift

dom/src/main/scala-2/org/scalajs/dom/DropEffectValue.scala

@@ -1,3 +1,5 @@
+package org.scalajs.dom
+
 import scala.scalajs.js
 
 @js.native

dom/src/main/scala-2/org/scalajs/dom/EffectAllowedValue.scala

@@ -1,3 +1,5 @@
+package org.scalajs.dom
+
 import scala.scalajs.js
 
 @js.native

dom/src/main/scala/org/scalajs/dom/DataTransferItem.scala

@@ -10,7 +10,7 @@ import scala.scalajs.js
 
 /** Each DataTransferItem object is associated with a [[DataTransfer]] object. */
 @js.native
-trait DataTransferItem {
+trait DataTransferItem extends js.Object {
 
   /** Returns the drag data item kind, one of: "string", "file". */
   def kind: DragDataItemKind = js.native

dom/src/main/scala/org/scalajs/dom/DataTransferItemList.scala

@@ -9,7 +9,7 @@ package org.scalajs.dom
 import scala.scalajs.js
 
 @js.native
-trait DataTransferItemList {
+trait DataTransferItemList extends js.Object {
 
   /** Returns the number of items in the drag data store. */
   def length: Int = js.native
@@ -29,10 +29,11 @@ trait DataTransferItemList {
 
   /** Removes all the entries in the drag data store. */
   def clear(): Unit = js.native
-}
 
-object DataTransferItemList {
+}
 
+@js.native
+object DataTransferItemList extends DataTransferItemList {
   /** Returns the DataTransferItem object representing the indexth entry in the drag data store. */
   def apply(index: Int): DataTransferItem = js.native
 }