C: add Glenn Lewis (Google CLA)

For work on goauth2.

LGTM=adg
R=adg
CC=golang-codereviews
https://golang.org/cl/110150043

CONTRIBUTORS

@@ -235,6 +235,7 @@ Georg Reinke <guelfey@gmail.com>
 Gerasimos Dimitriadis <gedimitr@gmail.com>
 Gideon Jan-Wessel Redelinghuys <gjredelinghuys@gmail.com>
 Giles Lean <giles.lean@pobox.com>
+Glenn Lewis <gmlewis@google.com>
 Gordon Klaus <gordon.klaus@gmail.com>
 Graham King <graham4king@gmail.com>
 Graham Miller <graham.miller@gmail.com>