OHHTTPStubs not working with watchOS

### New Issue Checklist

- [x] I have tried with the latest version of OHHTTPStubs
- [x] 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: 6.1.0
- integration method you are using:
* [x] Cocoapods
* [ ] Carthage
* [ ] submodule
* [ ] other
- version of the tool you use: 1.5.3

### Issue Description

Stubs are never considered for watchOS, same code runs fine in iOS.

### Steps to reproduce

1. Create an iOS + watchOS application
2. Add the following code in both apps, this should return empty data for all requests:
```
stub(condition: isScheme("http") || isScheme("https")) { _ in
return OHHTTPStubsResponse(data: Data(), statusCode: 200, headers: nil)
}
```
3. Add code to download any file and print contents

**Expectation**: Output should be empty in both apps (as the stubs are returning an empty data object)
**Results iOS**: Empty output is printed
**Results watchOS**: Actual file contents are printed, download was not stubbed

Can also be veryfied using breakpoints, for watchOS the return statement is never being called.