Update index.md

Change 'provider' to ProviderInterface::class in laravel/index.md

Author: noweh

laravel/index.md

@@ -243,6 +243,7 @@ Register the state provider:
 namespace App\Providers;
 
 use App\State\BookProvider;
++use ApiPlatform\State\ProviderInterface;
 use Illuminate\Contracts\Foundation\Application;
 use Illuminate\Support\ServiceProvider;
 
@@ -254,7 +255,7 @@ class ApiServiceProvider extends ServiceProvider
             return new BookProvider();
         });
 
-        $this->app->tag([BookProvider::class], 'provider');
+        $this->app->tag([BookProvider::class], ProviderInterface::class);
     }
 }
 ```