Fix node6 support for Object.entries and URL object (#548)

This patch introduces a polyfill for Object.entries which is missing in Node 6

lib/helper.js

@@ -218,4 +218,9 @@ class Helper {
   }
 }
 
+// Polyfill from https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/entries
+if (!Object.entries)
+  Object.entries = obj => Object.keys(obj).map(key => [key, obj[key]]);
+
+
 module.exports = Helper;