Remove todo adding deferred to service provider (#660)

Author: d8vjork

src/QueryBuilderServiceProvider.php

@@ -2,9 +2,10 @@
 
 namespace Spatie\QueryBuilder;
 
+use Illuminate\Contracts\Support\DeferrableProvider;
 use Illuminate\Support\ServiceProvider;
 
-class QueryBuilderServiceProvider extends ServiceProvider
+class QueryBuilderServiceProvider extends ServiceProvider implements DeferrableProvider
 {
     public function boot()
     {
@@ -26,8 +27,6 @@ public function register()
 
     public function provides()
     {
-        // TODO: implement DeferrableProvider when Laravel 5.7 support is dropped.
-
         return [
             QueryBuilderRequest::class,
         ];