Fixes a bug with date parsing on Safari

Safari didn't like the string we made and frankly once we stopped using
"month only" this is what we should have done initially.

Related to Issue #38

components/calendar/Controller.vue

@@ -40,9 +40,7 @@ export default Vue.extend({
 
   computed: {
     datetime(): string {
-      const month = (this.month).toString().padStart(2, '0');
-      // Passing with time is important, otherwise it's handled as UTC.
-      return `${this.year}-${month}-01 00:00:00`;
+      return new Date(this.year, this.month - 1).toISOString();
     },
     previousCalendar(): CalendarLinkInfo {
       return {