公式ブログ用：gulpfile.js : gulp-beautify

blog-nunjucks-parts03.js

// set:beautify_option 
const beautify_option = {
  'indent_size': 2
}

// task:nunjucks
gulp.task('nunjucks', function(){
  return gulp.src(paths.src.html + '**/*.njk')
  .pipe(data(function(){
    return require(paths.src.json);
  }))
  .pipe(nunjucks({
    path: paths.src.template
  }))
  .pipe(beautify(beautify_option))
  .pipe(gulp.dest(paths.dest.root))
});