[BUG] DatePicker: Uncaught TypeError

[JohnVillalovos]

[X]: This is a bug and not a question.

[X]: I understand that the best way to resolve this issue is to solve it and propose a Pull Request.

Describe the bug**

Uncaught TypeError: (inst.selectedMonth + 1).padStart is not a function
AddSpecificDate http://lb.int.sodarock.com/Web/scripts/schedule.js?v=3.0.1:1202
dpDateChanged http://lb.int.sodarock.com/Web/scripts/schedule.js?v=3.0.1:1215
jQuery 26
http://lb.int.sodarock.com/Web/view-schedule.php:3494
jQuery 13
schedule.js:1202:76

To Reproduce**

Steps to reproduce the behavior:

1. go to /Web/view-schedule.php (should be logged out)
2. click in Show/Hide Navigation if the calendar is not displayed
3. Check Show Specific Dates

4. Click on any date in the calendar, nothing happens and the console displays the error

Uncaught TypeError: (inst.selectedMonth + 1).padStart is not a function
AddSpecificDate http://lb.int.sodarock.com/Web/scripts/schedule.js?v=3.0.1:1202
dpDateChanged http://lb.int.sodarock.com/Web/scripts/schedule.js?v=3.0.1:1215
jQuery 26
http://lb.int.sodarock.com/Web/view-schedule.php:3494
jQuery 13
schedule.js:1202:76

Librebooking commit 23b4d6c