If you want to use CoffeeScript for Gulp config instead of JS.

gulpfile.js

// Require some necessary modules.
require('coffee-script');
var gutil = require('gulp-util');

// Specify, where is your Gulp config in CoffeeScript placed.
var gulpfile = 'Gulpfile.coffee';

// Print notification into the console. 
gutil.log('Using file', gutil.colors.magenta(gulpfile));

// Execute CoffeeScript config.
require('./' + gulpfile);

https://github.com/gulpjs/gulp/blob/master/docs/recipes/using-coffee-script-for-gulpfile.md