docs: function transformFile ({ config, entry, outdir }) {
    const filename = entry[0]
    const filepath = entry[1] || `${outdir}/${filename}`
    const results = babel.transform(
      fs.readFileSync(filename, 'utf8'),
      Object.assign({}, config, { filename, sourceMaps: true })
    )
    mkdirp.sync(path.dirname(filepath))
    fs.writeFileSync(
      filepath,
      results.code + '\n\n//# sourceMappingURL=' + path.basename(filepath)
    )
    fs.writeFileSync(`${filepath}.map`, JSON.stringify(results.map))
  
    return results
  }