message: [now-cli] Use `yarn` for `now dev` integration tests
  This was switched to `npm` for debugging purposes in but at this
  point we can switch it back to `yarn` so the tests don't take as long.
diff: @@ -116,10 +116,9 @@ async function exec(directory, args = []) {
  async function runNpmInstall(fixturePath) {
  if (await fs.exists(path.join(fixturePath, 'package.json'))) {
  - await execa('npm', ['install'], {
  + await execa('yarn', ['install'], {
  cwd: fixturePath,
  shell: true,
  - stdio: 'inherit',
  });
  }
  }
  