title: created_at and updated_at not working automatically in laravel 5.6 when use model::insert() . why?
body: <pre><code>ProductCategory::insert($insertData);
  </code></pre>
  
  <p>I am using this above statement passing an array for inserting multiple record <code>$insertData</code> working fine but when check my <code>created_at</code> and <code>updated_at</code> column not getting timestamp.</p>