Remove unstable version badge

Author: pionl

Diff for: readme.md

@@ -3,7 +3,6 @@
 [![Total Downloads](https://poser.pugx.org/pion/laravel-chunk-upload/downloads?format=flat)](https://packagist.org/packages/pion/laravel-chunk-upload)
 [![Build Status](https://github.com/pionl/laravel-chunk-upload/workflows/build/badge.svg)](https://github.com/pionl/laravel-chunk-upload/actions)
 [![Latest Stable Version](https://poser.pugx.org/pion/laravel-chunk-upload/v/stable?format=flat)](https://packagist.org/packages/pion/laravel-chunk-upload)
-[![Latest Unstable Version](https://poser.pugx.org/pion/laravel-chunk-upload/v/unstable?format=flat)](https://packagist.org/packages/pion/laravel-chunk-upload)
 [![License](https://poser.pugx.org/pion/laravel-chunk-upload/license)](https://packagist.org/packages/pion/laravel-chunk-upload)
 
 ## Introduction