Add `shortWeekDays` and `shortMonths` to it_IT.ts

[sberequek]

It's possible to add missing translation for shortWeekDays and shortMonths, in italian (itIT):

shortWeekDays: ['Dom', 'Lun', 'Mar', 'Mer', 'Gio', 'Ven', 'Sab'],
shortMonths: ['Gen', 'Feb', 'Mar', 'Apr', 'Mag', 'Giu', 'Lug', 'Ago', 'Set', 'Ott', 'Nov', 'Dic'],

[afc163]

PR welcome