Updated settings example in overriding templates docs.

Follow up to ba4389a36b5fb1afce0cddb4e28233138b6612b7.

docs/howto/overriding-templates.txt

@@ -29,7 +29,7 @@ called ``blog``, which provides the templates ``blog/post.html`` and
 
     from pathlib import Path
 
-    BASE_DIR = Path(__file__).resolve(strict=True).parents[1]
+    BASE_DIR = Path(__file__).resolve(strict=True).parent.parent
 
     INSTALLED_APPS = [
         ...,