Remove hint for old Laravel versions

Author: spawnia

README.md

@@ -15,15 +15,6 @@ Easily integrate [GraphQL Playground](https://github.com/prismagraphql/graphql-p
 
     composer require mll-lab/laravel-graphql-playground
 
-If you are using Laravel < 5.4, add the service provider to your `config/app.php`
-
-```php
-'providers' => [
-    // Other providers...
-    MLL\GraphQLPlayground\GraphQLPlaygroundServiceProvider::class,
-]
-```
-
 If you are using Lumen, register the service provider in `bootstrap/app.php`
 
 ```php