Made upsert return reference to created document

When upsert is true and it can't find an existing record to match the query, it calls self._insert which will return a ref to the newly created doc as the 2nd param to the callback, but the upsert logic wasn't catching a 2nd param (only the first param: err) so I just added the 2nd param as 'newDoc' and passed it to the upsert callback instead of 'true'.

lib/datastore.js

@@ -477,9 +477,9 @@ Datastore.prototype._update = function (query, updateQuery, options, cb) {
       } else {
         // The upserted document is the query (since for now queries have the same structure as
         // documents), modified by the updateQuery
-        return self._insert(model.modify(query, updateQuery), function (err) {
+        return self._insert(model.modify(query, updateQuery), function (err, newDoc) {
           if (err) { return callback(err); }
-          return callback(null, 1, true);
+          return callback(null, 1, newDoc);
         });
       }
     });