Update nlpworker.cpp

src/nlpworker.cpp

@@ -36,7 +36,7 @@ void heartbeat_timer(const boost::system::error_code & /*e*/,
 	else
 	{
 		std::cout << "Heartbeat failed. Exiting\n";
-		throw runtime_error("Heartbeat failed. Network error?");
+		throw std::runtime_error("Heartbeat failed. Network error?");
 	}