message: compile fix for boost 1.66 or gcc 7.3
diff: @@ -126,7 +126,7 @@ private:
  // The acceptor object used to accept incoming socket connections.
  boost::asio::ip::tcp::acceptor acceptor_;
  // To protect the list of messages...
  - boost::asio::strand strand_;
  + boost::asio::io_service::strand strand_;
  // To keep the io_service running...
  std::shared_ptr<boost::asio::io_service::work> work_;
  // The list of active connections
  