title: Incorrect weeks calculation in momentjs
body: <p>I use node.js with moment 2.9.0</p>
  
  <pre><code>var moment = require("moment");
  var d = moment.utc([2014, 11, 27]);
  var iso = d.toISOString();
  var week = d.week();
  </code></pre>
  
  <p>shows iso = "2014-12-27T00:00:00.000Z"
  and week is 52.</p>
  
  <p>But if <code>var d = moment.utc([2014, 11, 28]);</code></p>
  
  <p>iso is 2014-12-28T00:00:00.000Z</p>
  
  <p>week is 1. Why?</p>
  
  <p>Thank you.</p>