title: Date format when creating invoice
body: <p>When I try to create invoice using REST API I get validation error like:</p>
  
  <pre><code>"details":[{"field":"items.date","issue":"only date field allowed with (yyyy-MM-dd z) format. (was 2014-12-27T17:01:00Z)
  </code></pre>
  
  <p>I tried with 2014-12-27T17:01:00Z, 2014-12-27Z, and number of others, but I get always the same error.</p>
  
  <p>What kind of format should date be? Can you give me an example?</p>