Working with github enterprise

Is there a way to use this lib with Git-Hub Enterprise?

I tried this as below but it doesn't seem to work. Please let me know what I'm missing.

```
const token = process.env.GIT_API_TOKEN,
apiBase = 'https://git.company.com/api/v3',
GitHub = require('github-api'),
gh = new GitHub({ token, apiBase });

let me = gh.getUser();
me.listNotifications(function(err, notifications) {
console.log(notifications);
});
```

Start by reproducing the supplied JavaScript example against the GitHub Enterprise apiBase, then inspect how the GitHub constructor and listNotifications request use that setting. Confirm whether the request reaches the Enterprise endpoint and define done as successful notification retrieval or a documented, actionable limitation.

索引モデルが issue の本文から書いたものです。