_registerSummary() {
    this._inspector.on('end', () => {
      var numFiles = this._inspector.numFiles;
      var files = (numFiles > 1) ? 'files' : 'file';
      var matches = (this._found > 1) ? 'matches' : 'match';
      var summary;

      if (!this._found) {
        summary = chalk.green(util.format(
          '\nNo matches found across %d %s', numFiles, files));
      } else {
        summary = chalk.red(util.format('\n%d %s found across %d %s',
          this._found, matches, numFiles, files));
      }

      this._writableStream.write(summary + '\n');
    });
  }
Registers a listener that prints a final summary outlining the number of
matches detected, as well as the number of files analyzed.