fix add missing import to RelationshipsWithIncludes

Author: d8vjork

src/Http/Resources/RelationshipsWithIncludes.php

@@ -4,6 +4,7 @@
 
 use Illuminate\Database\Eloquent\Collection as DatabaseCollection;
 use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\Pivot;
 use Illuminate\Support\Arr;
 use Illuminate\Support\Collection;
 use Illuminate\Support\Str;