[8.x] Update the badges to use shields.io

(And keep the markdown syntax this time)

Author: pataar

README.md

@@ -1,9 +1,9 @@
 # Lumen PHP Framework
 
 [![Build Status](https://travis-ci.org/laravel/lumen-framework.svg)](https://travis-ci.org/laravel/lumen-framework)
-[![Total Downloads](https://poser.pugx.org/laravel/lumen-framework/d/total.svg)](https://packagist.org/packages/laravel/lumen-framework)
-[![Latest Stable Version](https://poser.pugx.org/laravel/lumen-framework/v/stable.svg)](https://packagist.org/packages/laravel/lumen-framework)
-[![License](https://poser.pugx.org/laravel/lumen-framework/license.svg)](https://packagist.org/packages/laravel/lumen-framework)
+[![Total Downloads](https://img.shields.io/packagist/dt/laravel/framework)](https://packagist.org/packages/laravel/lumen-framework)
+[![Latest Stable Version](https://img.shields.io/packagist/v/laravel/framework)](https://packagist.org/packages/laravel/lumen-framework)
+[![License](https://img.shields.io/packagist/l/laravel/framework)](https://packagist.org/packages/laravel/lumen-framework)
 
 Laravel Lumen is a stunningly fast PHP micro-framework for building web applications with expressive, elegant syntax. We believe development must be an enjoyable, creative experience to be truly fulfilling. Lumen attempts to take the pain out of development by easing common tasks used in the majority of web projects, such as routing, database abstraction, queueing, and caching.