title: SimpleDateFormat("yyyyMMd‌dHH:mm:ss") has issue on groovy
body: <p>I call groovy script in Jenkins pipeline.</p>
  
  <pre><code>def start_time = new Date()
  def sdf = new SimpleDateFormat("yyyyMMd‌​dHH:mm:ss")
  println sdf.format(start_time)
  </code></pre>
  
  <p>But I get "20160817‌​1708:34:35", the day has been output twice.
  So I test it on my local machine with groovy, and I get the same result.</p>
  
  <p>Any thing I missed?</p>