Add vish to contributors.

R=r, rsc
http://go/go-review/1026012
diff --git a/CONTRIBUTORS b/CONTRIBUTORS
index f761977..850b012 100644
--- a/CONTRIBUTORS
+++ b/CONTRIBUTORS
@@ -47,3 +47,4 @@
 Scott Schwartz <scotts@golang.org>
 Stephen Ma <stephenm@golang.org>
 Tom Szymanski <tgs@google.com>
+Vish Subramanian <vish@google.com>