Add missing callback on close of hijacked connections

vendor/github.com/vulcand/oxy/forward/fwd.go

@@ -363,7 +363,12 @@ func (f *httpForwarder) serveWebSocket(w http.ResponseWriter, req *http.Request,
 				ctx.errHandler.ServeHTTP(w, req, errHijack)
 				return
 			}
-			defer conn.Close()
+			defer func() {
+				conn.Close()
+				if f.websocketConnectionClosedHook != nil {
+					f.websocketConnectionClosedHook(req, conn)
+				}
+			}()
 
 			errWrite := resp.Write(conn)
 			if errWrite != nil {