gulp-rigger
Rigger is a build time include engine for Javascript, CSS, CoffeeScript and in general any type of text file that you wish to might want to "include" other files into.
Install with npm.
npm install --save-dev gulp-rigger
var gulp = require('gulp');
var rigger = require('gulp-rigger');
gulp.task('default', function () {
gulp.src('app/*.js')
.pipe(rigger())
.pipe(gulp.dest('build/'));
});