[css-sizing-4] Add Jen to editors list

Author: fantasai

css-sizing-4/Overview.bs

@@ -10,6 +10,7 @@ ED: https://drafts.csswg.org/css-sizing
 TR: https://www.w3.org/TR/css-sizing/
 Editor: Tab Atkins, Google, http://xanthir.com/contact/, w3cid 42199
 Editor: Elika J. Etemad / fantasai, Invited Expert, http://fantasai.inkedblade.net/contact, w3cid 35400
+Editor: Jen Simmons, Mozilla, http://jensimmons.com/
 Previous version: https://www.w3.org/TR/2012/WD-css3-sizing-20120927/
 Abstract: This is a delta spec over CSS Sizing Level 3.
 Ignored Terms: block-level box