Examples. Fix compilation

Author: turansky

examples/browser/src/jsMain/kotlin/example/EventHandler.kt

@@ -5,6 +5,7 @@ import web.dom.Document
 import web.dom.document
 import web.events.addEventHandler
 import web.events.addHandler
+import web.uievents.DRAG_OVER
 import web.uievents.DragEvent
 
 private fun preventDefaultExample_handler() {