[Whiteboard] Fix nginx conf to enable websocket

pica-whiteboard/default.conf

@@ -15,5 +15,8 @@ server {
 		proxy_set_header Host $host;
 		proxy_set_header X-Real-IP $remote_addr;
 		proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+		proxy_http_version 1.1;
+		proxy_set_header Upgrade $http_upgrade;
+		proxy_set_header Connection upgrade;
 	}
 }