DO NOT EDIT CORE FILES LIKE THAT
NO! Never. 1989danielb please do not suggest that. It's a terrible idea, all your changes will be lost when you upgrade and your site will break.
Okay. Now that we're all NOT editing core....
You can move the wp-config.php file one level up. So if you install WP here:
The config can go in the NON web-accessible folder:
However. The concept that renaming that file will 'help' is not actually so. First of all, you have to be able to have a 'common' file to tell WP 'this is where I live' and since WP is open source, any reasonable hacker would be able to write a script that checks what your site is calling instead of wp-config.php
Sometimes intruder coming to my server and use symlink to read any wp-config.php files in whole server.
THIS is bad, horrible, dear god get a new webhost, levels of security holes. A GOOD server does not allow user A to read ANY files from User B. A symlink could be made, but would be unreadable because of permissions.
And still, renaming won't matter if I can run a server side scan for all files with the wp-config 'headers'
Unless of course the intruder gets in with root access, at which point nothing matters at all.