fix(webpack.config.dev): ship polyfills in dev mode as well.

Author: halfzebra

config/webpack.config.dev.js

@@ -46,6 +46,8 @@ module.exports = {
   // This means they will be the "root" imports that are included in JS bundle.
   // The first two entry points enable "hot" CSS and auto-refreshes for JS.
   entry: [
+    // We ship a few polyfills by default:
+    require.resolve('./polyfills'),
     // Include an alternative client for WebpackDevServer. A client's job is to
     // connect to WebpackDevServer by a socket and get notified about changes.
     // When you save a file, the client will either apply hot updates (in case