message: Update README.md example programs
  fix
diff: @@ -186,6 +186,7 @@ Example HTTP program:
  ```C++
  #include <beast/http.hpp>
  #include <boost/asio.hpp>
  +#include <boost/lexical_cast.hpp>
  #include <iostream>
  #include <string>
  @@ -200,18 +201,19 @@ int main()
  r.resolve(boost::asio::ip::tcp::resolver::query{host, "http"}));
  // Send HTTP request using beast
  - beast::http::request_v1<beast::http::empty_body> req;
  + beast::http::request<beast::http::empty_body> req;
  req.method = "GET";
  req.url = "/";
  req.version = 11;
  - req.headers.replace("Host", host + ":" + std::to_string(sock.remote_endpoint().port()));
  - req.headers.replace("User-Agent", "Beast");
  + req.fields.replace("Host", host + ":" +
  + boost::lexical_cast<std::string>(sock.remote_endpoint().port()));
  + req.fields.replace("User-Agent", "Beast");
  beast::http::prepare(req);
  beast::http::write(sock, req);
  // Receive and print HTTP response using beast
  beast::streambuf sb;
  - beast::http::response_v1<beast::http::streambuf_body> resp;
  + beast::http::response<beast::http::streambuf_body> resp;
  beast::http::read(sock, sb, resp);
  std::cout << resp;
  }
  