Fix a Dockerfile linter
Fix a Dockerfile linter

Thanks @loburm for rebasing to distroless!
kawych/k8s-stackdriver,GoogleCloudPlatform/k8s-stackdriver,GoogleCloudPlatform/k8s-stackdriver,kawych/k8s-stackdriver,GoogleCloudPlatform/k8s-stackdriver,kawych/k8s-stackdriver,kawych/k8s-stackdriver