message: Use Envoy::ProtobufTypes::String instead of std::string.
diff: @@ -144,8 +144,10 @@ void CreateCheckRequest::setHttpRequest(
  auto mutable_headers = httpreq.mutable_headers();
  headers.iterate(
  [](const Envoy::Http::HeaderEntry& e, void* ctx) {
  - Envoy::Protobuf::Map<::std::string, ::std::string>* mutable_headers =
  - static_cast<Envoy::Protobuf::Map<::std::string, ::std::string>*>(ctx);
  + Envoy::Protobuf::Map<Envoy::ProtobufTypes::String, Envoy::ProtobufTypes::String>*
  + mutable_headers = static_cast<
  + Envoy::Protobuf::Map<Envoy::ProtobufTypes::String, Envoy::ProtobufTypes::String>*>(
  + ctx);
  (*mutable_headers)[e.key().getString()] = e.value().getString();
  return Envoy::Http::HeaderMap::Iterate::Continue;
  },
  