fix(queryhelpers): remove Object.values() for Node.js 4.x-6.x support

Re: #8596

Author: vkarpov15

lib/queryhelpers.js

@@ -21,7 +21,8 @@ const clone = require('./helpers/clone');
  */
 
 exports.preparePopulationOptions = function preparePopulationOptions(query, options) {
-  const pop = Object.values(query.options.populate);
+  const _populate = query.options.populate;
+  const pop = Object.keys(_populate).reduce((vals, key) => vals.concat([_populate[key]]), []);
 
   // lean options should trickle through all queries
   if (options.lean != null) {
@@ -43,7 +44,8 @@ exports.preparePopulationOptions = function preparePopulationOptions(query, opti
  */
 
 exports.preparePopulationOptionsMQ = function preparePopulationOptionsMQ(query, options) {
-  const pop = Object.values(query._mongooseOptions.populate);
+  const _populate = query._mongooseOptions.populate;
+  const pop = Object.keys(_populate).reduce((vals, key) => vals.concat([_populate[key]]), []);
 
   // lean options should trickle through all queries
   if (options.lean != null) {