Restore tag.
diff --git a/.hgtags b/.hgtags
index 92f0c54..d9240f3 100644
--- a/.hgtags
+++ b/.hgtags
@@ -80,3 +80,4 @@
 35efb1054ec6ceca72017a587263cb6a9257340b v3.1.1rc1
 8b9c0f573ab29c41c6c5fdcca82a1fe0ff5355af v3.1.1
 c4eba5a6f81e332f65a806efb528758857389fd7 v3.1.1
+21ac16cb23077b1e7fa34dffeb53f6aafe4b336d v3.1.1