code: function filterBefore(posts) {
        before = moment(before.replace(/\//g, '-'), 'MM-DD-YYYY', true);
        if (!before.isValid()) {
          console.log(chalk.red('Before date is not valid (expecting `MM-DD-YYYY`), ignoring argument.'));
          return posts;
        }
  
        return posts.filter(function filterPosts(post) {
          return moment(post.date).isBefore(before);
        });
      }
docs: filter the posts using a before date if supplied