code: function(inDir, outDir){
      var name = this.bundleOptions.name;
      var opts = this._generateEsperantoOptions(name);
      var transpilerName = formatToFunctionName[this.format];
      var targetExtension = this.targetExtension;
  
      return esperanto.bundle({
        base: inDir,
        entry: this.bundleOptions.entry
      }).then(function(bundle) {
        var compiledModule = bundle[transpilerName](opts);
        var fullOutputPath = path.join(outDir, name + '.' + targetExtension);
  
        return writeFile(fullOutputPath, compiledModule.code);
      });
    }
docs: A hook called if ES6Modules is being used in a n-to-1 bundle.
  
  Begins importing at an entry point and adds a single bundled
  module to the output tree.