config: null uri props in nerf-dart

Deleting the properties will not work anymore in io.js 2.0 as the
properties are now getters/setters and deleting them will delete the
getters/setters themselves from the instance. Nulling the properties has
the same effect, while also bringing a performance gain over delete.

Related: nodejs/node#1591

lib/config/nerf-dart.js

@@ -13,11 +13,11 @@ module.exports = toNerfDart
  */
 function toNerfDart(uri) {
   var parsed = url.parse(uri)
-  delete parsed.protocol
-  delete parsed.auth
-  delete parsed.query
-  delete parsed.search
-  delete parsed.hash
+  parsed.protocol = null
+  parsed.auth = null
+  parsed.query = null
+  parsed.search = null
+  parsed.hash = null
 
   return url.resolve(url.format(parsed), ".")
 }