code: function getShortChunkName (source) {
    if (source.match(relativePkg) || path.isAbsolute(source)) {
      return path.dirname(source).split(path.sep).slice(-2).join('/') + '/' + path.basename(source)
    }
    else {
      return source
    }
  }
docs: shortens the chunk name to its parent directory basename and its basename