title: jQuery doesn't fire $.ajax.fail() when Mockjax returns status:500 (or 400 or...)
body: <p>Mockjax setup: </p>
  
  <pre><code>$.mockjax({
    url: "/api/get",
    responseTime: 100, // default: 500
    dataType: "json",
    data: { action: "all" },
    proxy: "data.json",
    status: 400
  });
  </code></pre>
  
  <p>The call to mockjax:</p>
  
  <pre><code>$.ajax({
    url: '/api/get',
    dataType: "json",
    data: { action: "all" }
  })
  .always(function() {
    //something
  })
  .done(function(json) {
    console.log("done");
  })
  .fail(function() {
    console.log("error");
  });
  </code></pre>
  
  <p>The mockjax properly returns the (JSON) data, but <strong>the problem is</strong> that always the <code>done()</code> callback is called (and never the <code>fail()</code>), regardless of mockjax status number set.</p>
  
  <p>But if I intentionally set the bad proxy path, only then the <code>fail()</code> is fired.</p>
  
  <p>What gives?</p>