[css-grid] Add Rachel and Jen to the acknowledgements that clearly haven't been updated in awhile...

Author: fantasai

css-grid/Overview.bs

@@ -4248,6 +4248,7 @@ Acknowledgements</h2>
 
 	This specification is made possible by input from
 	Erik Anderson,
+	Rachel Andrew,
 	Rossen Atanassov,
 	Manuel Rego Casasnovas,
 	Arron Eicholz,
@@ -4262,6 +4263,7 @@ Acknowledgements</h2>
 	Mats Palmgren,
 	François Remy,
 	Sergio Villar Senin,
+	Jen Simmons,
 	Christian Stockwell,
 	Eugene Veselov,
 	and the CSS Working Group members,