Requests error out when the body is not json

Evaluate the following:

```
(tentacles.pulls/specific-pull "Malabarba" "lazy-map-clojure" 1 {:accept "application/vnd.github.VERSION.patch"})
```

You'll immediately get an exception because the `:body` is a patch file, and `parse-safe` tries to parse it as json.

Thanks for this great package!
