Problem with case-sensitive filesystem

I was running openapi2yaml on MacOS, and it generates files such as "query.json" for a component "Query" entity. But then it emits a reference form like `"$ref": "Query.json"` which causes problems with de-referencing.

Also, when I try to build a standalone JSON schema, I conjecture that this causes a problem. I see output like this:

```
Generating interpretation.json
An error occured processing interpretation: URLError:
```