applets/digital-clock: Fix `Qt.formatDateTime` returns different date when minute changes

Qt.formatDateTime uses MM instead of mm to represent month number.

When minute changes, log using console.log(main.lastDate, currentDate, dataSource.data["Local"]["DateTime"]); in dateTimeChanged()

Before:

2022-24-4 2022-25-4 周五 3月 4 10:25:01 2022 GMT+0800

After:

2022-3-4 2022-3-4 周五 3月 4 10:25:01 2022 GMT+0800