async function workaroundEmptyStyleChunk (stats, outDir) {
  const styleChunk = stats.children[0].assets.find(a => {
    return /styles\.\w{8}\.js$/.test(a.name)
  })
  if (!styleChunk) return
  const styleChunkPath = path.resolve(outDir, styleChunk.name)
  const styleChunkContent = await fs.readFile(styleChunkPath, 'utf-8')
  await fs.remove(styleChunkPath)
  // prepend it to app.js.
  // this is necessary for the webpack runtime to work properly.
  const appChunk = stats.children[0].assets.find(a => {
    return /app\.\w{8}\.js$/.test(a.name)
  })
  const appChunkPath = path.resolve(outDir, appChunk.name)
  const appChunkContent = await fs.readFile(appChunkPath, 'utf-8')
  await fs.writeFile(appChunkPath, styleChunkContent + appChunkContent)
}
find and remove empty style chunk caused by
https://github.com/webpack-contrib/mini-css-extract-plugin/issues/85
TODO remove when it's fixed

@param {Object} stats
@param {String} outDir
@returns {Promise<void>}