Asynchronous Stup without a callback

### New Issue Checklist

- [X] I have tried with the latest version of OHHTTPStubs
- [ ] I have read the [README](https://github.com/AliSoftware/OHHTTPStubs/blob/master/README.md)
- [X] I have read the [Using the right Swift Version of `OHHTTPStubs` for your project](https://github.com/AliSoftware/OHHTTPStubs#using-the-right-swift-version-of-ohhttpstubs-for-your-project) section
- [X] I have searched in the [existing issues](https://github.com/AliSoftware/OHHTTPStubs/issues?utf8=✓&q=is%3Aissue)
- [X] I have read [the OHHTTPStubs wiki](https://github.com/AliSoftware/OHHTTPStubs/wiki) to see if there wasn't a detailed page talking about my issue

### Environment

- version of OHHTTPStubs: [LIB VERSION HERE]
- integration method you are using:
* [ ] Cocoapods
* [X] Carthage
* [ ] submodule
* [ ] other
- version of the tool you use: [INSERT VERSION HERE]

### Issue Description

How can I use OHTTPStub for a method that is asynchronous but doesn't have a callback?
I have research on the internet and I could not find an answer.

##### Complete output when you encounter the issue (if any)

```
[INSERT OUTPUT HERE]
```