Add to upgrade instructions.

upgrade.md

@@ -4,4 +4,5 @@
 
 - `composer update`.
 - Replace `public/index.php`, `artisan.php`.
-- Add new `expire_on_close` option to `session` configuration file.
+- Add new `expire_on_close` option to `session` configuration file.
+- Remove call to `redirectIfTrailingSlash` in `bootstrap/start.php` file.