Fixes go lint warning.

Change-Id: I5a7485a4c8316b81e6aa50b95fe75e424f2fcedc
Reviewed-on: https://go-review.googlesource.com/109055Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>