I know this is not using moment, however this is in the format you want
Check this out.
http://jsfiddle.net/robbmj/czu6scth/2/
window.onload = function() {
      var display = document.querySelector('#time'),
          timer = new CountDownTimer(5);
      timer.onTick(format).onTick(restart).start();
      function restart() {
        if (this.expired()) {
          setTimeout(function() { timer.start(); }, 1000);
        }
      }
      function format(minutes, seconds) {
        minutes = minutes < 10 ? "0" + minutes : minutes;
        seconds = seconds < 10 ? "0" + seconds : seconds;
        display.textContent = minutes + ':' + seconds;
      }
    };
This will display in  00:00 format.