refactor: use require.resolve instead of a relative path

I don't know if it makes any difference but the dependency relationship
looks clearer to me after the change.

recommended.js

@@ -1,6 +1,6 @@
 module.exports = {
   extends: [
-    './index.js',
+    require.resolve('./index'),
     'plugin:@typescript-eslint/recommended'
   ],