Fix da lang: Months and days should be lowercase

Month and day names should be lowercase in Danish.

Please refer to [sproget.dk](http://sproget.dk/raad-og-regler/ordlister/sproglige-ordlister/store-eller-sma-begyndelsesbogstaver-i-proprier-tiltalepronomener-og-titulaturer) and [Retskrivningsordbogen](http://www.dsn.dk/)