fix: checking of closure instance

Author: yajra

src/Html/Button.php

@@ -2,6 +2,7 @@
 
 namespace Yajra\DataTables\Html;
 
+use Closure;
 use Illuminate\Contracts\Support\Arrayable;
 use Illuminate\Support\Fluent;
 use Illuminate\Support\Traits\Macroable;