[css-sizing-3] Add dholbert and mats to acknowledgements.

Author: fantasai

css-sizing-3/Overview.bs

@@ -1089,7 +1089,12 @@ Changes</h2>
 <h2 class=no-num id="acknowledgments">
 Acknowledgments</h2>
 
-	<p>Special thanks go to Aaron Gustafson, L. David Baron
+	<p>Special thanks go to
+	L. David Baron,
+	Aaron Gustafson,
+	Daniel Holbert,
+	and
+	Mats Palmgren
 	for their contributions to this module.
 
 <h2 class=no-num id=priv-sec>