Fixed the two broken references to SweetAlert (#3943)

* Fixed the two broken references to SweetAlert

The urls I used where the best ones I managed to find. (I'm sure there are better ones somewhere, but it was surprisingly difficult finding them.)

* Changed the urls again

examples/timeline/editing/editingItemsCallbacks.html

@@ -10,8 +10,8 @@
     }
   </style>
 
-  <script src="http://t4t5.github.io/sweetalert/dist/sweetalert.min.js"></script>
-  <link href="http://t4t5.github.io/sweetalert/dist/sweetalert.css" rel="stylesheet" type="text/css"/>
+  <script src="https://cdn.jsdelivr.net/npm/sweetalert@1.1.3/dist/sweetalert.min.js"></script>
+  <link href="https://cdn.jsdelivr.net/npm/sweetalert@1.1.3/dist/sweetalert.css" rel="stylesheet" type="text/css"/>
 
   <script src="../../../dist/vis.js"></script>
   <link href="../../../dist/vis-timeline-graph2d.min.css" rel="stylesheet" type="text/css" />
@@ -138,4 +138,4 @@
 
 </script>
 </body>
-</html>
+</html>