Update editor's affilitation (#508)

index.bs

@@ -9,7 +9,7 @@ Group: texttracks
 ED: https://w3c.github.io/webvtt/
 TR: https://www.w3.org/TR/webvtt1/
 Level: none
-Editor: Gary Katsevman, Brightcove Inc. https://www.brightcove.com/, w3c@gkatsev.com
+Editor: Gary Katsevman, Mux Inc. https://www.mux.com/, w3c@gkatsev.com
 Former Editor: Silvia Pfeiffer, NICTA CSIRO https://www.csiro.au/, silviapfeiffer1@gmail.com
 Former Editor: Simon Pieters, Opera Software AS http://www.opera.com/, simonp@opera.com
 Former Editor: Philip Jägenstedt, Opera Software ASA http://www.opera.com/, philipj@opera.com