message: fix json export uint32_t
diff: @@ -365,6 +365,8 @@ inline void to_json(JSON &j, const Any &a)
  j = a.get<bool>();
  else if (a.is<uint8_t>())
  j = a.get<uint8_t>();
  + else if (a.is<uint32_t>())
  + j = a.get<uint32_t>();
  else if (a.is<float>())
  j = a.get<float>();
  else if (a.is<std::string>())
  