docs: replace folder with directory

For consistency.

Author: kenjis

user_guide_src/source/concepts/autoloader.rst

@@ -59,7 +59,7 @@ The value is the location to the directory the classes can be found in.
 
     > php spark namespaces
 
-By default, the application folder is namespace to the ``App`` namespace. You must namespace the controllers,
+By default, the application directory is namespace to the ``App`` namespace. You must namespace the controllers,
 libraries, or models in the application directory, and they will be found under the ``App`` namespace.
 
 You may change this namespace by editing the **app/Config/Constants.php** file and setting the