Fix compilation error on windows

lib/request.cpp

@@ -226,7 +226,7 @@ Request &Request::connection_timeout(long t) {
 #elif defined(TCP_MAXRT)
     curl_easy_setopt(this->easy, CURLOPT_SOCKOPTFUNCTION, [](void *clientp, curl_socket_t sock, curlsocktype) -> int {
         unsigned int maxrt = static_cast<Request *>(clientp)->connection_timeout_ /*s*/;
-        setsockopt(sock, IPPROTO_TCP, TCP_MAXRT, &maxrt, sizeof(maxrt));
+        setsockopt(sock, IPPROTO_TCP, TCP_MAXRT, (const char *)&maxrt, sizeof(maxrt));
         return CURLE_OK;
     });
     curl_easy_setopt(this->easy, CURLOPT_SOCKOPTDATA, this);