code: function listFiles(directory) {
      return fs.lstatAsync(directory)
          .then(lstat => lstat.isDirectory() ? fs.readdirAsync(directory) : [])
          .catchReturn([]);
  }
docs: Returns all the files in a directory if it exists. Otherwise, return an
  empty array as fallback (everything inside a promise)
  
  @param {String} directory
  @return {String[]}