Update index.d.ts

Added dayjsLocalizer type that was added in this PR: jquense/react-big-calendar#2264

Author: levani132

types/react-big-calendar/index.d.ts

@@ -554,6 +554,7 @@ export function luxonLocalizer(
     firstDayOfWeek: number;
   },
 ): DateLocalizer;
+export function dayjsLocalizer(dayjs: object): DateLocalizer;
 
 export const Navigate: {
     PREVIOUS: 'PREV';