Investigate `endOfInputError`

Here is the error message:

```
2019-12-26T19:11:06.085383+00:00 app[web.1]: [Error]   [26-12-2019 18:40:29.700] [Hintman.Webhook.prReviewHook#94] [ThreadId 125] Failed to fetch PR deltas: endOfInput
```

And this is the PR:

* https://github.com/kowainik/ilist/pull/6