candidate fix for issue #3 using optimist

I am sorry, I wasn't able in any way to update the existing issue with the pull request.
```
curl -u  "danse" --request POST        --data '{"issue":"3", "head": "danse:optimist", "base": "davidchambers:master", "title":"a possible fix"}'        https://api.github.com/repos/davidchambers/doctest/pulls;
Enter host password for user 'danse':
{
  "errors": [
    {
      "field": "issue",
      "code": "unauthorized",
      "resource": "PullRequest"
    }
  ],
  "message": "Validation Failed"
}
```