fix webpack.config.js sample typing

api/extension-guides/web-extensions.md

@@ -119,7 +119,9 @@ The webpack configuration file is automatically generated by `yo code`. It bundl
 const path = require('path');
 const webpack = require('webpack');
 
-const webExtensionConfig = /** @type WebpackConfig */ {
+/** @typedef {import('webpack').Configuration} WebpackConfig **/
+/** @type WebpackConfig */
+const webExtensionConfig = {
   mode: 'none', // this leaves the source code as close as possible to the original (when packaging we set this to 'production')
   target: 'webworker', // extensions run in a webworker context
   entry: {