yyyy in date_format_base.dart must be in uppercase

[Tzanou123]

The String yyyy (from line 10 of date_format_base) return "yyyy" but when i call the date i get 10/05/yyyy if i replace it by "YYYY" it is working as expected

[tejainece]

print(formatDate(DateTime(1989, 2, 21), [dd, '/', mm, '/', yyyy])); correctly prints 21/02/1989.

Please feel free to reopen the issue with more information.