code: function sortPosts (posts) {
    return Object.keys(posts).map(function (post) { return posts[post]; })
      .sort(function (a,b) {
        if ( a.date < b.date ) return 1;
        if ( a.date > b.date ) return -1;
        return 0;
      });
  }
docs: Takes an array `posts` of post objects and returns a
  new, sorted version based off of date
  
  @params {Array} posts
  @returns {Array}