title: Convert date from unix format to ISO8601
body: <p>I'm storing the timestamps as UTC unix epoch time.</p>
  
  <p>I want to convert that time to ISO 8601 format. (<code>2013-08-01T05:14:48Z</code>)</p>
  
  <p>For example, unix epoch time of <code>1375334088</code> means <code>Thu, 01 Aug 2013 05:14:48 GMT</code>.</p>
  
  <p>But when I do <code>date('c', 1375334088)</code> it gives <code>2013-08-01T06:14:48+01:00</code> instead of <code>2013-08-01T05:14:48Z</code></p>