function runLintingOnDirectory(relativePath) {
  return new Promise((resolve, reject) => {
    shell.exec(
      `npm run lint:eslint "app/${relativePath}/**/**.js"`,
      {
        silent: true,
      },
      code =>
        code
          ? reject(new Error(`Linting error(s) in ${relativePath}`))
          : resolve(relativePath),
    );
  });
}
Run eslint on all js files in the given directory
@param {string} relativePath
@returns {Promise<string>}