code: func makeVersionFile(relPath string, versionFile pkg.VersionFile) (fs.File, error) {
  	if !fs.IsCleanSlashPath(relPath) {
  		return nil, fmt.Errorf("invalid version_file: %s", relPath)
  	}
  	blob, err := json.MarshalIndent(versionFile, "", "  ")
  	if err != nil {
  		return nil, err
  	}
  	return &blobFile{
  		name: relPath,
  		blob: blob,
  	}, nil
  }
docs: // makeVersionFile returns File representing a JSON blob with info about package
  // version. It's what's deployed at path specified in 'version_file' stanza in
  // package definition YAML.