title: Get grandparent directory name in gulp
body: <p>I'm tying to get get the grandparentparent directory of my <code>gulpfile.js</code> file.
  This is my folder structure : <code>airi\Gulp\gulpfile.js</code> 
  I want to get the folder with name <code>airi</code>.</p>
  
  <pre><code>gulp.task('serve', ['sass'], function () {
      browserSync.init({
          proxy: "http://localhost/" + var_that_stores_name_airi,
      });
  });
  </code></pre>
  
  <p><code>var_that_stores_name_airi</code> would be my variable that contains the folder name I want ( ie: airi ).I want this so that I can append it my browsersync proxy url.
  How do I do this in gulp ? Thanks </p>