Do not try to include Node's fs module

This was caused by rdflib now `require`ing solid-auth-cli, which
Webpack then tried to bundle. Since that code path should never be
hit in production, we can safely exclude it from the bundle.

Author: Vinnl

webpack.config.js

@@ -30,4 +30,7 @@ module.exports = {
     }),
     new ForkTsCheckerWebpackPlugin(),
   ],
-};
+  node: {
+    fs: 'empty'
+  }
+}