fixed dict merging for Python 3.8

nicegui/client.py

@@ -71,7 +71,7 @@ class Client:
     def build_response(self, request: Request, status_code: int = 200) -> Response:
         prefix = request.headers.get('X-Forwarded-Prefix', request.scope.get('root_path', ''))
         elements = json.dumps({id: element._to_dict() for id, element in self.elements.items()})
-        socket_io_js_query_params = globals.socket_io_js_query_params | {'client_id': self.id}
+        socket_io_js_query_params = {**globals.socket_io_js_query_params, **{'client_id': self.id}}
         vue_html, vue_styles, vue_scripts, imports, js_imports = generate_resources(prefix, self.elements.values())
         return templates.TemplateResponse('index.html', {
             'request': request,