docs: update stable version number

Author: streamtw

README.md

@@ -3,7 +3,7 @@
 <p align="center">
   <a target="_blank" href="https://packagist.org/packages/unisharp/laravel-filemanager"><img src="https://poser.pugx.org/unisharp/laravel-filemanager/downloads"></a>
   <a target="_blank" href="https://packagist.org/packages/unisharp/laravel-filemanager"><img src="https://img.shields.io/packagist/dm/unisharp/laravel-filemanager.svg"></a>
-  <a target="_blank" href="https://packagist.org/packages/unisharp/laravel-filemanager"><img src="https://img.shields.io/badge/stable-2.3.0-blue.svg"></a>
+  <a target="_blank" href="https://packagist.org/packages/unisharp/laravel-filemanager"><img src="https://img.shields.io/badge/stable-2.4.0-blue.svg"></a>
   <a target="_blank" href="https://packagist.org/packages/unisharp/laravel-filemanager"><img src="https://poser.pugx.org/unisharp/laravel-filemanager/license"></a>
   <br>
   <a href="https://github.styleci.io/repos/39873788?branch=master"><img src="https://github.styleci.io/repos/39873788/shield?branch=master" alt="StyleCI"></a>