Get critical styles via Gulp

getcriticalstyles.js

var penthouse = require('penthouse');
var Promise = require("bluebird");
var penthouseAsync = Promise.promisify(penthouse);

gulp.task('critical', function(){
  penthouseAsync({
    url : 'http://daverupert.com/',
    css : './stylesheets/style.css',
    height: 480
  }).then( function (criticalCSS){
    require('fs').writeFile('_includes/critical.css', criticalCSS );
  });
});