remove post-check and pre-check - discouraged IE-only Cache directives (#205)

Author: marjatech

core/files/var/www/html/index.php

@@ -1,7 +1,7 @@
 <?php
 $proto = (isset($_SERVER['SERVER_PROTOCOL']))?($_SERVER['SERVER_PROTOCOL']):('HTTP/1.1');
 header($proto.' 503 Service Unavailable', true);
-header('cache-control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0');
+header('cache-control: no-store, no-cache, must-revalidate');
 header('retry-after: 30');
 header('refresh: 30');
 ?>