Added instruction to update composer.json to 4.1

upgrade.md

@@ -2,6 +2,7 @@
 
 ## Upgrading From 4.0 to 4.1
 
+- Update `composer.json` to require `"laravel/framework": "4.1.*"` 
 - `composer update`.
 - Replace `public/index.php`, `artisan.php`.
 - Add new `expire_on_close` option to `session` configuration file.