Fix test in Firefox

scalajs-dom is incorrect:
scala-js/scala-js-dom#219

Author: japgolly

test/src/test/scala/japgolly/scalajs/react/extra/EventListenerTest.scala

@@ -3,7 +3,7 @@ package japgolly.scalajs.react.extra
 import japgolly.scalajs.react._
 import japgolly.scalajs.react.test.ReactTestUtils
 import japgolly.scalajs.react.vdom.prefix_<^._
-import org.scalajs.dom.Event
+import org.scalajs.dom.document
 import utest._
 import TestUtil._
 
@@ -20,7 +20,7 @@ object EventListenerTest extends TestSuite {
     val c = ReactTestUtils.renderIntoDocument(C())
 
     def dispatch(name: String) = {
-      val e = new Event
+      val e = document.createEvent("Event")
       e.initEvent(name, true, true)
       ReactDOM findDOMNode c dispatchEvent e
     }