WebSocket: server and client handlers now equal

Since anmonteiro/httpun-ws#39, the equality
of the server and client connection handler types has been exposed. Can
now use Dream's connection handlers directly, without an Obj.magic
cast.

See also aantron/dream#181.

src/http/websocket.ml

@@ -105,7 +105,7 @@ let ws socket request =
       Message.response ~status:`Switching_Protocols Stream.empty Stream.null in
     let (_, server_stream) = Message.create_websocket response in
     Lwt.wakeup_later receive_response response;
-    Dream_httpaf.Websocket.client_websocket_handler server_stream socket
+    Dream_httpaf.Websocket.websocket_handler server_stream socket
   in
 
   let%lwt client =