Update Chairs

removed Kristina Yasuda as co-Chair of the group; updated Brent Zundel's email address.

index.md

@@ -7,5 +7,5 @@ _The mission of the Verifiable Credentials (formerly known as Verifiable Claims)
 
 _The Working Group is now in maintenance mode._
 
-_The Chairs of the Working Group are [Kristina Yasuda](mailto:Kristina.Yasuda@microsoft.com) and [Brent Zundel](mailto:brent.zundel@evernym.com). The W3C Staff Contact for the Working Group is [Ivan Herman](mailto:ivan@w3.org)._
+_The Chair of the Working Group is [Brent Zundel](mailto:brent.zundel@gmail.com). The W3C Staff Contact for the Working Group is [Ivan Herman](mailto:ivan@w3.org)._