Minor style change.

Change-Id: Ib30243a71a83de1a67d3d005bfdd1e04265fca1e
GitHub-Last-Rev: 9d654de10eaa6f01ece29790fb81bc41dfd61eaf
GitHub-Pull-Request: golang/go#31479
Reviewed-on: https://go-review.googlesource.com/c/go/+/172199Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Sameer Ajmani <sameer@golang.org>