officehours: use cached URL

layouts/shortcodes/officehours.html

@@ -7,7 +7,7 @@
         </tr>
     </thead>
     <tbody>
-    {{ $appointments := getJSON "https://sprechstunden.stusta.de/manyappointments.json" }}
+    {{ $appointments := getJSON "https://stustanet.de/api/officehours.json" }}
     {{ range first 5 $appointments }}
         <tr>
             <td>{{ if (eq $.Site.Language.Lang "de") }}