Fix standalone build

package.json

@@ -1,6 +1,6 @@
 {
   "name": "fimfic2epub",
-  "version": "1.7.28",
+  "version": "1.7.29",
   "description": "Tool to generate improved EPUB ebooks from Fimfiction stories",
   "author": "djazz",
   "license": "MIT",

webpack.config.babel.js

@@ -202,6 +202,19 @@ const bundleStaticNpmModuleConfig = {
 
   module: {
     rules: [
+      {
+        test: /\.js$/,
+        loader: 'babel-loader',
+        exclude: /node_modules/,
+        query: {
+          sourceMaps: !inProduction,
+          presets: [['env', {
+            targets: {
+              node: 'current'
+            }
+          }]]
+        }
+      },
       {
         test: /\.styl$/,
         use: ['raw-loader', 'stylus-loader']