[css-transitions-1] Update editors list

Add Brian Birtles to list of editors, move David Hyatt and Chris Marrin
to list of former editors.

Author: birtles

css-transitions-1/Overview.bs

@@ -34,8 +34,9 @@ Previous version: https://www.w3.org/TR/2013/WD-css3-transitions-20131119/
 ED: https://drafts.csswg.org/css-transitions/
 Editor: L. David Baron, Mozilla https://www.mozilla.org/, https://dbaron.org/, w3cid 15393
 Editor: Dean Jackson, Apple Inc https://www.apple.com/, dino@apple.com, w3cid 42080
-Editor: David Hyatt, Apple Inc https://www.apple.com/, hyatt@apple.com, w3cid 34140
-Editor: Chris Marrin, Apple Inc https://www.apple.com/, cmarrin@apple.com
+Editor: Brian Birtles, Mozilla https://www.mozilla.org/, bbirtles@mozilla.com, w3cid 43194
+Former Editor: David Hyatt, Apple Inc https://www.apple.com/, hyatt@apple.com, w3cid 34140
+Former Editor: Chris Marrin, Apple Inc https://www.apple.com/, cmarrin@apple.com
 Issue Tracking: Bugzilla bugs for this level https://www.w3.org/Bugs/Public/buglist.cgi?query_format=advanced&product=CSS&component=Transitions&resolution=---&status_whiteboard=defer%20to%20level%202&status_whiteboard_type=notregexp
 Issue Tracking: Bugzilla bugs for all levels https://www.w3.org/Bugs/Public/buglist.cgi?query_format=advanced&product=CSS&component=Transitions&resolution=---
 Abstract: CSS Transitions allows property changes in CSS values to occur smoothly over a specified duration.