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

test/specs/__helpers.js

@@ -1,3 +1,6 @@
+// Polyfill ES6 Promise
+require('es6-promise').polyfill();
+
 // Polyfill URLSearchParams
 URLSearchParams = require('url-search-params');