fix: correct implementation of createAppointment

Makes the suggested implementation of `createAppointment` correctly handle appointment creations that
cross timezones - e.g. due to Daylight Savings Time.

re: https://forum.exercism.org/t/tests-and-suggested-implementation-for-appointment-time-are-wrong/

Author: BadIdeaException

exercises/concept/appointment-time/.meta/exemplar.js

@@ -9,7 +9,10 @@
  * @returns {Date} the appointment
  */
 export function createAppointment(days, now = Date.now()) {
-  return new Date(now + days * 24 * 3600 * 1000);
+  const date = new Date(now);
+  date.setDate(date.getDate() + days);
+
+  return date;
 }
 
 /**
@@ -73,7 +76,7 @@ export function updateAppointment(timestamp, options) {
 export function timeBetween(timestampA, timestampB) {
   return Math.round(
     (new Date(timestampB).getTime() - new Date(timestampA).getTime()) / 1000,
-  );
+    );
 }
 
 /**