code: function StatsPlugin (output, options, cache) {
    this.output = output
    this.options = options
    this.cache = cache
  }
docs: Create a new StatsPlugin that causes webpack to generate a stats file as
  part of the emitted assets.
  @constructor
  @param {String} output Path to output file.
  @param {Object} options Options passed to the stats' `.toJson()`.