git-codereview: fix vet warning to fix build on Go 1.10
git-codereview: fix vet warning to fix build on Go 1.10

Change-Id: Ib4cee24d5b70f99dfbebf0aa05c85be6164ba835
Reviewed-on: https://go-review.googlesource.com/84216
Run-TryBot: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

golang/review