We update [`StopwatchPanel`](https://github.com/mozilla-b2g/gaia/blob/3f51f302c3a0c57d8bad482ec7ee86b2819389fb/apps/clock/js/stopwatch_panel.js) to use this instead of [`StopwatchPanel#hms`](https://github.com/mozilla-b2g/gaia/blob/3f51f302c3a0c57d8bad482ec7ee86b2819389fb/apps/clock/js/stopwatch_panel.js#L171-L197)