Update index.html

public/index.html

@@ -10,8 +10,8 @@
             content="width=device-width, initial-scale=1, maximum-scale=1, minimum-scale=1, user-scalable=no">
         <title>Meidling 3D Viewer</title>
         <!-- The Cesium library. -->
-       <script src="https://cesiumjs.org/releases/1.57/Build/Cesium/Cesium.js"></script>
-        <link href="https://cesiumjs.org/releases/1.57/Build/Cesium/Widgets/widgets.css" rel="stylesheet">
+       <script src="https://cesium.com/downloads/cesiumjs/releases/1.81/Build/Cesium/Cesium.js"></script>
+        <link href="https://cesium.com/downloads/cesiumjs/releases/1.81/Build/Cesium/Widgets/widgets.css" rel="stylesheet">
         <!-- stylesheets -->
 		<link rel="stylesheet" href="./CSS/index.css" media="screen">
 		<link rel="stylesheet" type="text/css" href="./CSS/meidling.css">