title: using moment.js to display duration in format 00:XX when duration is less than an hour
body: <p>I'm trying to format a countdown timer using moment duration format
  but as soon as time hits below 60 minutes , the hours disappear
  e.g. 60 minutes display as "01:00"
  which is correct
  59 minutes display as  "59" 
  which is not correct, it should display as "00:59"</p>
  
  <p>where 3500000 milliseconds is equal to 58 minutes</p>
  
  <p>I have the following code:</p>
  
  <pre><code>moment.duration(3500000).format("hh:mm", { forceLength: true })
  </code></pre>
  
  <p>which displays result : 58, rather than 00:58</p>
  
  <p>what am I doing wrong here ?</p>
  
  <p>I have also attempted the variation to no avail</p>
  
  <pre><code>moment.duration(3500000).format("HH:mm", { forceLength: true })
  </code></pre>