docs: update apache docs link

Author: kenjis

user_guide_src/source/general/environments.rst

@@ -49,7 +49,7 @@ Apache
 ------
 
 This server variable can be set in your **.htaccess** file or Apache
-config using `SetEnv <https://httpd.apache.org/docs/2.2/mod/mod_env.html#setenv>`_.
+config using `SetEnv <https://httpd.apache.org/docs/2.4/mod/mod_env.html#setenv>`_.
 
 .. code-block:: apache