Fix issues with duplicate polyfill added with 16

Signed-off-by: Julius Härtl <jus@bitgrid.net>

js/.babelrc.js

@@ -0,0 +1,12 @@
+module.exports = {
+	presets: [
+		[
+			'@babel/preset-env',
+			{
+				targets: {
+					browsers: ['last 2 versions', 'ie >= 11']
+				}
+			}
+		]
+	]
+}

js/webpack.config.js

@@ -2,14 +2,12 @@ const path = require('path');
 const webpack = require('webpack');
 const MiniCssExtractPlugin = require('mini-css-extract-plugin');
 
-require('babel-polyfill');
-
 module.exports = {
   node: {
     fs: 'empty',
   },
   entry: {
-    deck: ['babel-polyfill', './init.js'],
+    deck: ['./init.js'],
   },
   output: {
     filename: '[name].js',