Make debug builds opt-in

If you want a debug build, set NODE_ENV=development. I added this just
in case someone forgets to set the mode, like in the Ultraviolet-Static
repository.

bundle.js

@@ -6,7 +6,6 @@ const __dirname = path.resolve(path.dirname(decodeURI(new URL(import.meta.url).p
 console.log(path.resolve(path.dirname(decodeURI(new URL(import.meta.url).pathname))), __dirname);
 
 webpack({
-    mode: 'none',
     entry: path.join(__dirname, './rewrite/index.js'),
     output: {
         path: __dirname,