Make CakePHP ignore config folder of either case

This takes the change from #339 and makes it case insensitive so that CakePHP projects from both before and after the rename ignore the appropriate files.

CakePHP.gitignore

 tmp/*
-Config/core.php
-Config/database.php
+[Cc]onfig/core.php
+[Cc]onfig/database.php
 app/tmp/*
-app/Config/core.php
-app/Config/database.php
+app/[Cc]onfig/core.php
+app/[Cc]onfig/database.php
 !empty