Changed the iso8601Week function of the Datepicker interface to return type 'number', not type 'void'. See: http://api.jqueryui.com/datepicker/

jqueryui/jqueryui.d.ts

@@ -157,7 +157,7 @@ declare module JQueryUI {
         setDefaults(defaults: DatepickerOptions): void;
         formatDate(format: string, date: Date, settings?: DatepickerFormatDateOptions): string;
         parseDate(format: string, date: string, settings?: DatepickerFormatDateOptions): Date;
-        iso8601Week(date: Date): void;
+        iso8601Week(date: Date): number;
         noWeekends(): void;
     }