docs: add missing 4

Author: kenjis

user_guide_src/source/installation/upgrade_controllers.rst

@@ -16,7 +16,7 @@ What has been changed
 
 - Since namespaces have been added to CodeIgniter 4, the controllers must be changed to support namespaces.
 - Controllers don't use constructors any more (to invoke CI 'magic') unless those are part of base controllers you make.
-- CI provides Request and Response objects for you to work with - more powerful than the CI3-way.
+- CI4 provides Request and Response objects for you to work with - more powerful than the CI3-way.
 - If you want a base controller (``MY_Controller`` in CI3), make it where you like,
   e.g., BaseController extends Controller, and then have your controllers extend it