Merge pull request #109 from LLK/greenkeeper/xhr-2.4.0

Update xhr to the latest version 

package.json

@@ -68,6 +68,6 @@
     "webpack": "2.2.1",
     "webpack-combine-loaders": "2.0.3",
     "webpack-dev-server": "2.4.1",
-    "xhr": "2.3.3"
+    "xhr": "2.4.0"
   }
 }