Call context cancel function after shutdown.

Keeps go vet from complaining.

webserver.go

@@ -473,6 +473,7 @@ func serveGroupRecordings(w http.ResponseWriter, r *http.Request, f *os.File, gr
 }
 
 func shutdown() {
-	ctx, _ := context.WithTimeout(context.Background(), 2*time.Second)
+	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
+	defer cancel()
 	server.Shutdown(ctx)
 }