unix: run go fix

Generated by running:

    go fix ./...

Change-Id: I4dab4582f1bdee9fc44710b8d10ca2dd9989f49d
Reviewed-on: https://go-review.googlesource.com/c/sys/+/821060
Auto-Submit: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
LUCI-TryBot-Result: golang-scoped@luci-project-accounts.iam.gserviceaccount.com <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>