[css-cascade] Update spec metadata

Author: xfq

css-cascade-3/Overview.bs

@@ -3,13 +3,13 @@ Title: CSS Cascading and Inheritance Level 3
 Shortname: css-cascade
 Level: 3
 Status: ED
-Deadline: 2015-07-15
 Work Status: Testing
 Group: csswg
 ED: https://drafts.csswg.org/css-cascade-3/
 TR: https://www.w3.org/TR/css-cascade-3/
 Editor: Elika J. Etemad / fantasai, Invited Expert, http://fantasai.inkedblade.net/contact, w3cid 35400
 Editor: Tab Atkins Jr., Google, http://xanthir.com/contact/, w3cid 42199
+Previous Version: https://www.w3.org/TR/2018/CR-css-cascade-3-20180828/
 Previous Version: https://www.w3.org/TR/2016/CR-css-cascade-3-20160519/
 Previous Version: https://www.w3.org/TR/2015/CR-css-cascade-3-20150416/
 Previous Version: https://www.w3.org/TR/2013/WD-css-cascade-3-20130730/