Date Picker: NgbCalendarGregorian is not in public api.

[itayod]

Bug description:

Hi, I am trying to use the NgbCalendarGregorian, but it seems to not be in your public api.
I need to use this class for a factory method that need to return MyCustomCalendar or NgbCalendarGregorian (as the default calendar).

I will be glad if it will be part of the public api or maybe show me some work around that I have maybe missed.

p.s. I will be happy to create a pr for it 😄

Versions of Angular, ng-bootstrap and Bootstrap:

Angular: 7.2.5

ng-bootstrap: 4.0.2

[maxokorokov]

NgbCalendarGregorian is the one used by default, so you shouldn't do anything special to use it. But this is definitely an omission, we should add it to public exports in src/index.ts and src/datepicker/datepicker.module.ts

[itayod]

Thank you @maxokorokov ,

Actually I am using it inside a factory method that should return CustomCalendar or the default calendar,
and also my CustomCalendar extends NgbCalendarGregorian.

Anyway thanks for the quick fix 🎉🎉