rename cache keys.

src/main/resources/static/index.html

@@ -21,7 +21,7 @@
 
 <script type="text/javascript">
     let websocket = null;
-    let key = "U_C_0_9";
+    let key = "$SS:C_0_9";
     let token = "8fde06cd6b5d488b92aa2053eea2949c";
 
     function openWebSocket() {