src/cli/util.js/createIgnorer
function createIgnorer(context) {
  const ignoreFilePath = path.resolve(context.argv["ignore-path"]);
  let ignoreText = "";

  try {
    ignoreText = fs.readFileSync(ignoreFilePath, "utf8");
  } catch (readError) {
    if (readError.code !== "ENOENT") {
      context.logger.error(
        `Unable to read ${ignoreFilePath}: ` + readError.message
      );
      process.exit(2);
    }
  }

  return ignore().add(ignoreText);
}