Update filter documentation. (#363)

* Update filter documentation.

Custom filter implementations should return an instance of `\Illuminate\Database\Eloquent\Builder`.

* Update filtering.md

Author: denisrpriebe

docs/features/filtering.md

@@ -142,7 +142,7 @@ use Illuminate\Database\Eloquent\Builder;
 
 class FiltersUserPermission implements Filter
 {
-    public function __invoke(Builder $query, $value, string $property) : Builder
+    public function __invoke(Builder $query, $value, string $property)
     {
         $query->whereHas('permissions', function (Builder $query) use ($value) {
             $query->where('name', $value);