Replace obsolete utime() usage with utimes().

This fixes build time warnings with POSIX.1-2008-aware c libraries.
diff --git a/src/dnsmasq.c b/src/dnsmasq.c
index 045489f..b985b79 100644
--- a/src/dnsmasq.c
+++ b/src/dnsmasq.c
@@ -1375,7 +1375,7 @@
 	/* update timestamp file on TERM if time is considered valid */
 	if (daemon->back_to_the_future)
 	  {
-	     if (utime(daemon->timestamp_file, NULL) == -1)
+	     if (utimes(daemon->timestamp_file, NULL) == -1)
 		my_syslog(LOG_ERR, _("failed to update mtime on %s: %s"), daemon->timestamp_file, strerror(errno));
 	  }
 #endif