Simplify code for cookie dir

See https://github.com/FreshRSS/FreshRSS/issues/700
See https://github.com/FreshRSS/FreshRSS/commit/eec95ffb6a414f00f0ddd6cb1f81ac7ee55d4f6b

lib/Minz/Session.php

@@ -65,9 +65,9 @@ class Minz_Session {
 	 * @param $l la durée de vie
 	 */
 	public static function keepCookie($l) {
-		// Get the script_name (e.g. /p/i/index.php) and remove index.php
+		// Get the script_name (e.g. /p/i/index.php) and keep only the path.
 		$cookie_dir = empty($_SERVER['SCRIPT_NAME']) ? '' : $_SERVER['SCRIPT_NAME'];
-		$cookie_dir = substr($cookie_dir, 0, -strlen(basename($cookie_dir)));
+		$cookie_dir = dirname($cookie_dir);
 		session_set_cookie_params($l, $cookie_dir, '', false, true);
 	}