Date-fns localizer - display weekDayFormat correctly (#2568)

Changed the weekdayFormat to be consistent with the dayjs localizer.

Author: islami00

src/localizers/date-fns.js

@@ -23,7 +23,7 @@ let weekRangeFormat = ({ start, end }, culture, local) =>
 export let formats = {
   dateFormat: 'dd',
   dayFormat: 'dd eee',
-  weekdayFormat: 'cccc',
+  weekdayFormat: 'ccc',
 
   selectRangeFormat: timeRangeFormat,
   eventTimeRangeFormat: timeRangeFormat,