cloudbuild: fix import path
This is an artifact of generating cloudbuild with manually-modified path before
cl/269598918 was submitted.
//
// For information about setting deadlines, reusing contexts, and more
// please visit godoc.org/cloud.google.com/go.
-package cloudbuild // import "cloud.google.com/go/devtools/cloudbuild/apiv1"
+package cloudbuild // import "cloud.google.com/go/cloudbuild/apiv1"
import (
"context"
