add babel polyfill to webpack

webpack.config.dev.js

@@ -3,7 +3,7 @@ require('dotenv').config();
 
 module.exports = {
 	devtool: 'cheap-module-eval-source-map',
-	entry: ['webpack-hot-middleware/client',
+	entry: ['babel-polyfill', 'webpack-hot-middleware/client',
           './client/index.js',
   ],
   output: {

webpack.config.prod.js

@@ -10,6 +10,7 @@ module.exports = {
   devtool: 'hidden-source-map',
 
   entry: [
+    'babel-polyfill',
     './client/index.js'
   ],