error in readme; Reading JSON using the pull interface

[Ryder17z]

Reading JSON using the pull interface
https://github.com/kazuho/picojson#reading-json-using-the-pull-interface

std::string json = "[ "hello JSON" ]";
picojson::value v;
std::string err = picojson::parse(v, json);
if (! err.empty()) {
std:cerr << err << std::endl;
}