Reference Resolution error

Hi there!

I love the idea of a validation proxy and tried it with an OpenAPI 3 spec used by our team.

I am getting the following error and hope you have an idea how to tackle this.

```
$ npx openapi-cop -s path-to-openapi.yaml -h 8888 -t https://localhost:8083
Validating against openapi.yaml ("API Specification", version: 0.1.0)
RangeError: Maximum call stack size exceeded
at /Volumes/some/repo/node_modules/swagger-client/dist/index.js:1:21167
at tryCatch (/Volumes/some/repo/node_modules/babel-runtime/node_modules/regenerator-runtime/runtime.js:62:40)
```

And then further down..

```
Failed to run openapi-cop Reference resolution error: Error: Could not resolve references in OpenAPI document due to the following errors:
[
{},
{}
]
✨ Done in 5.05s.
```