Revert "Update Webpack + deps, remove now unnecessary polyfills" (#2479)

* Revert "Update Webpack + deps, remove now unnecessary polyfills (#2410)"

This reverts commit 189b34c45a.

* Fix build (#2496)

* Change syntax to see if build passes

* Test commit

* Test with node 10

* Test adding all browsers in travis

* remove other browsers when running on travis

lib/helpers/buildURL.js

@@ -39,7 +39,7 @@ module.exports = function buildURL(url, params, paramsSerializer) {
         return;
       }
 
-      if (Array.isArray(val)) {
+      if (utils.isArray(val)) {
         key = key + '[]';
       } else {
         val = [val];