[css-values-5] Add Sebastian Zartner to acknowledgements.

Author: fantasai

css-values-5/Overview.bs

@@ -2432,9 +2432,9 @@ Acknowledgments</h2>
 	of this module.
 
 	Secondly, we would like to acknowledge
-	L. David Baron
-	and
-	Mike Bremford
+	L. David Baron,
+	Mike Bremford,
+	and Sebastian Zartner
 	for their comments and suggestions,
 	which have improved Level 5.