title: Add "ON DELETE CASCADE" to existing column in Laravel
body: <p>I have user_id fk column in my table</p>
  
  <pre><code>$table-&gt;foreign('user_id')-&gt;references('id')-&gt;on('users');
  </code></pre>
  
  <p>I should add <strong>on cascade delete</strong> feature to this existing column. How can I do this?</p>