Just noticed that running `./scripts/release/build.js -v 16.1.1` gives me:

```
 ERROR  ENOTDIR: not a directory, open '/Users/gaearon/p/react/packages/.DS_Store/package.json'

Error: 
    at Object.fs.openSync (fs.js:653:18)
    at fs.readFileSync (fs.js:554:33)
    at readdirSync.filter.dir (/Users/gaearon/p/react/scripts/release/utils.js:31:36)
    at Array.filter (<anonymous>)
    at getPublicPackages (/Users/gaearon/p/react/scripts/release/utils.js:29:36)
```

We should ignore system directories there.
const {frames, interval} = dots;
  let index = 0;
  const inProgressMessage = `- this may take a few ${
    isLongRunningTask ? 'minutes' : 'seconds'
  }`;
  const id = setInterval(() => {
    index = ++index % frames.length;
    logUpdate(
      `${chalk.yellow(frames[index])} ${text} ${chalk.gray(inProgressMessage)}`
    );
  }, interval);
  try {
    const returnValue = await promise;
    clearInterval(id);
    logUpdate(`${chalk.green('✓')} ${text}`);
    logUpdate.done();
    return returnValue;
  } catch (error) {
    logUpdate.clear();
    throw error;
  }
};
module.exports = {
  execRead,
  execUnlessDry,
  getPublicPackages,
  getUnexecutedCommands,
  logPromise,
};