title: Laravel 5.3 date validator: equal to or after start_date
body: <p>I'm using Laravel 5.3 to validate start_date and end_date for an event.
  end_date should be equal to start_date or the after date. <code>end_date &gt;= start_date</code></p>
  
  <pre><code>$validator = Validator::make($data, [
      'start_date'    =&gt; 'required|date',
      'end_date'      =&gt; 'required|date|after:start_date',
  ]);
  </code></pre>
  
  <p>I tried to use <strong>after</strong>, but it only works for end_date > start_date.
  Of course, I can add custom rule using <code>Validator::extend</code>, but I'd like to know if we can do without adding custom rule.</p>
  
  <p>Is there any way to add negative rule or add >= rule?</p>
  
  <p>Thanks</p>