[css-counter-styles-3] Update Previous Versions

Author: xfq

css-counter-styles-3/Overview.bs

@@ -7,6 +7,7 @@ Work Status: Testing
 Group: csswg
 ED: https://drafts.csswg.org/css-counter-styles/
 TR: https://www.w3.org/TR/css-counter-styles-3/
+Previous Version: https://www.w3.org/TR/2017/CR-css-counter-styles-3-20171214/
 Previous Version: https://www.w3.org/TR/2015/CR-css-counter-styles-3-20150611/
 Previous Version: https://www.w3.org/TR/2014/WD-css-counter-styles-3-20140826/
 Previous Version: https://www.w3.org/TR/2013/WD-css-counter-styles-3-20130718/