reporter(reporter: string | () => void, reporterOptions: {}): MochaWebpack {
    this.options = {
      ...this.options,
      reporter,
      reporterOptions,
    };
    return this;
  }
Set reporter to `reporter`, defaults to "spec".

@param {string|Function} reporter name or constructor
@param {Object} reporterOptions optional options
@return {MochaWebpack}