win, test: fix compilation warning

uv_os_fd_t is HANDLE on Windows, but closesocket needs a SOCKET.

PR-URL: https://github.com/libuv/libuv/pull/534
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

test/test-tcp-write-fail.c

@@ -43,7 +43,7 @@ static void close_socket(uv_tcp_t* sock) {
   r = uv_fileno((uv_handle_t*)sock, &fd);
   ASSERT(r == 0);
 #ifdef _WIN32
-  r = closesocket(fd);
+  r = closesocket((uv_os_sock_t)fd);
 #else
   r = close(fd);
 #endif