[css-text] fix punctuation

Author: upsuper

css-text/Overview.bs

@@ -2272,7 +2272,7 @@ Acknowledgements</h2>
   Hickson, Martin Heijdra, Richard Ishida, Masayasu Ishikawa,
   Michael Jochimsen, Eric LeVine, Ambrose Li, Håkon Wium Lie, Chris Lilley,
   Ken Lunde, Nat McCully, IM Mincheol, Shinyu Murakami, Paul Nelson,
-  Chris Pratley, Xidorn Quan Marcin Sawicki,
+  Chris Pratley, Xidorn Quan, Marcin Sawicki,
   Arnold Schrijver, Rahul Sonnad, Alan Stearns, Michel Suignard, Takao Suzuki,
   Frank Tang, Chris Thrasher, Etan Wexler, Chris Wilson, Masafumi Yabe
   and Steve Zilles.