Refactor window wrapper for node testing

src/core/window.js

@@ -1,3 +1,4 @@
+function makeWindow() {
   var win = {
     location: {},
     history: {},
@@ -5,6 +6,10 @@ var win = {
     close: () => {}
   }
 
+  if(typeof window === "undefined") {
+    return win
+  }
+
   try {
     win = window
     var props = ["File", "Blob", "FormData"]
@@ -17,4 +22,7 @@ try {
     console.error(e)
   }
 
-export default win
+  return win
+}
+
+module.exports = makeWindow()