add Sam Thorogood (of Google Inc.) to CONTRIBUTORS

R=r
CC=golang-dev
https://golang.org/cl/890048
diff --git a/CONTRIBUTORS b/CONTRIBUTORS
index 963a908..886a3d1 100644
--- a/CONTRIBUTORS
+++ b/CONTRIBUTORS
@@ -103,6 +103,7 @@
 Roger Peppe <rogpeppe@gmail.com>
 Ross Light <rlight2@gmail.com>
 Russ Cox <rsc@golang.org>
+Sam Thorogood <thorogood@google.com>
 Scott Schwartz <scotts@golang.org>
 Sergei Skorobogatov <skorobo@rambler.ru>
 Sergey 'SnakE' Gromov <snake.scaly@gmail.com>