Fix: image name for staging
As detailed in #137 (closed), we weren't deploying correctly. And until #106 (closed) is
completed, we need to deploy staging from the builder
image, rather
than the root image.
As detailed in #137 (closed), we weren't deploying correctly. And until #106 (closed) is
completed, we need to deploy staging from the builder
image, rather
than the root image.