read = function read(filename, callback) {
  return fs.readFile(filename, function (err, data) {
    if (err) return callback(err);
    return zlib.gunzip(data, function (err, content) {
      if (err) return callback(err);
      var result = {};

      try {
        result = JSON.parse(content);
      } catch (e) {
        return callback(e);
      }

      return callback(null, result);
    });
  });
}
Read the contents from the compressed file.

@async
@params {String} filename
@params {Function} callback