Shift deprecated helpers

Laravel recommends using the `Str` and `Arr` class methods directly instead of the respective helper functions. These helper functions are [deprecated in Laravel 5.8][1] and will be removed in a future version.

[1]: https://github.com/laravel/framework/pull/26898

app/Http/Middleware/Http2ServerPush.php

@@ -13,6 +13,7 @@
 
 namespace App\Http\Middleware;
 
+use Illuminate\Support\Str;
 use Closure;
 use Illuminate\Http\Request;
 use Illuminate\Http\Response;
@@ -119,7 +120,7 @@ class Http2ServerPush
         ];
 
         $type = collect($linkTypeMap)->first(function ($type, $extension) use ($url) {
-            return str_contains(strtoupper($url), $extension);
+            return Str::contains(strtoupper($url), $extension);
         });
 
         return is_null($type) ? null : "<{$url}>; rel=preload; as={$type}";