temp fix for offline exam url

src/features/OfflineExam/OfflineExamList.vue

@@ -190,7 +190,7 @@ export default {
       window.name = JSON.stringify(user);
       window.location.href =
         TK_SERVER_HTML_URL +
-        "admin/preview_paper/" +
+        "/admin/preview_paper/" +
         course.paperId +
         "?isback=true";
     },