[web-animations-2] Update editors (w3c#6699)

* Update editors on web-animations-2.

The web-animations-1 editors went through an update and it seems that
web-animations-2 should follow along.

* Update Brian's affiliation

Co-authored-by: Robert Flack <flackr@chromium.org>
Co-authored-by: Brian Birtles <birtles@gmail.com>

Author: flackr

web-animations-2/Overview.bs

@@ -34,9 +34,10 @@ Group: csswg
 Repository: w3c/csswg-drafts
 !Issue Tracking: <a href="https://github.com/w3c/csswg-drafts/labels/web-animations-2">GitHub</a>
 
-Editor: Brian Birtles 43194, Mozilla, bbirtles@mozilla.com
-Editor: Shane Stephens 47691, Google Inc, shans@google.com
-Editor: Douglas Stockwell, Google Inc, dstockwell@google.com
+Editor: Brian Birtles 43194, Invited Expert, brian@birchill.co.jp
+Editor: Robert Flack 98451, Google Inc, flackr@google.com
+Former Editor: Shane Stephens 47691, Google Inc, shans@google.com
+Former Editor: Douglas Stockwell, Google Inc, dstockwell@google.com
 Abstract: This specification defines a model for synchronization and
     timing of changes to the presentation of a Web page.
     This specification also defines an application programming interface