setDefaults() {
    this.modules = 'bootstrap';
    this.moduleName = 'default';
    this.outputLanguage = 'es5';
    this.referrer = '';
    this.sourceMaps = false;
    this.sourceRoot = false;
    this.lowResolutionSourceMap = false;
    this.inputSourceMap = false;
  }
Set values for non-boolean options.  Some non-boolean options allow
boolean values.