title: Validate a timestamp value in laravel 5
body: <p>I'm writing validator rules for checking if the data is valid before adding a new Eloquent model record.</p>
  
  <p>It's quite clear with strings, decimals and integers.</p>
  
  <p>But what about a timestamp field?</p>
  
  <p>I added the column using <code>timestamp</code> method in one of my DB migrations, it works just fine. The only thing I need is to make sure the passed value will be a valid timestamp before executing the query.</p>
  
  <p>Is there a direct/simple way or should I write a regexp for that?</p>
  
  <p>Thank you</p>