npm install --save-dev gulp-posthtml
Install required PostHTML plugins separately.
var posthtml = require('gulp-posthtml');
var gulp = require('gulp');
gulp.task('posthtml', function () {
var plugins = [
require('posthtml-doctype')('<!DOCTYPE html>'),
require('posthtml-custom-elements')()
];
var options = { closingSingleTag: 'slash' };
return gulp.src('./html/*.html')
.pipe(posthtml(plugins, options))
.pipe(gulp.dest('./dest'));
});