The `vinyl-ftp` package has a function [`clean()`](https://github.com/morris/vinyl-ftp#connclean-globs-local-options-) but I'm not sure how to use it right. I need to:

1. get all files from my `build` folder
2. put them into the target folder on my ftp server
3. clean files if they're not available locally

I have the following gulp task:

```
gulp.task('deploy', () => {
  let conn = ftp.create({host:host,user:user,password: password});
  return gulp.src('build/**', {base: './build/', buffer: false })
      .pipe(conn.newer('/path/on/my/server/')) // only upload newer files
      .pipe(conn.dest('/path/on/my/server/'))
      .pipe(conn.clean('build/**', './build/'));
});

```

1) and 2) is OK, but the `clean()` function does nothing