[selectors-4] Update last publication URL

Author: fantasai

selectors-4/Overview.bs

@@ -7,6 +7,7 @@ Status: ED
 Work Status: Refining
 ED: https://drafts.csswg.org/selectors/
 TR: https://www.w3.org/TR/selectors-4/
+Previous Version: https://www.w3.org/TR/2018/WD-selectors-4-20181121/
 Previous Version: https://www.w3.org/TR/2018/WD-selectors-4-20180202/
 Previous Version: https://www.w3.org/TR/2018/WD-selectors-4-20180201/
 Previous Version: https://www.w3.org/TR/2013/WD-selectors4-20130502/