docs(aio): Upgrade server-side rendering example to Angular V6 (#23649)

PR Close #23649

aio/content/examples/universal/webpack.server.config.js

@@ -5,8 +5,9 @@ module.exports = {
   entry: { server: './server.ts' },
   resolve: { extensions: ['.js', '.ts'] },
   target: 'node',
+  mode: 'none',
   // this makes sure we include node_modules and other 3rd party libraries
-  externals: [/(node_modules|main\..*\.js)/],
+  externals: [/node_modules/],
   output: {
     path: path.join(__dirname, 'dist'),
     filename: '[name].js'