Clean up typo in chat websocket javascript client

It so happened that the code works, because both variables exist,
but the code was not clean.

close #1620

CHANGELOG.md

@@ -4,6 +4,7 @@ Version 258:
 * Fix clang inititalization warning in websocket
 * Remove redundant use of `yield_to` in parser tests
 * Add VS 2019 AzP CI matrix item
+* Clean up typo in chat websocket javascript client
 
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example/websocket/server/chat-multi/chat_client.html

@@ -51,7 +51,7 @@
     };
     sendMessage.onkeyup = function(ev) {
       ev.preventDefault();
-      if (event.keyCode === 13) {
+      if (ev.keyCode === 13) {
         send.click();
       }
     }