title: D3.js utcParse() returns null
body: <p>I've got a date format which looks like this: <code>2017-02-18T09:00:00+06:00</code>.</p>
  
  <p>This is the format I'm trying to parse it with: <code>d3.utcParse("%Y-%m-%dT%H:%M:%S+%Z");</code>, but it returns <code>null</code>. </p>
  
  <p>Any ideas? Thanks! </p>