message: lightstep: fix string temporary issue
diff: @@ -21,8 +21,9 @@ LightstepHttpTracerFactory::createHttpTracer(const Json::Object& json_config,
  Upstream::ClusterManager& cluster_manager) {
  std::unique_ptr<lightstep::LightStepTracerOptions> opts(new lightstep::LightStepTracerOptions());
  - const auto access_token_sv =
  - StringUtil::rtrim(server.api().fileReadToEnd(json_config.getString("access_token_file")));
  + const auto access_token_file =
  + server.api().fileReadToEnd(json_config.getString("access_token_file"));
  + const auto access_token_sv = StringUtil::rtrim(access_token_file);
  opts->access_token.assign(access_token_sv.data(), access_token_sv.size());
  opts->component_name = server.localInfo().clusterName();
  