Fix casing consistency of $TAB on login page (hestiacp#2883)

This was made lowercase in hestiacp#926, not sure why.

Author: AlecRust

web/login/index.php

@@ -6,8 +6,7 @@
 
 include($_SERVER['DOCUMENT_ROOT'] . '/inc/main.php');
 
-$TAB = 'login';
-
+$TAB = 'LOGIN';
 
 if (isset($_GET['logout'])) {
     unset($_SESSION);