fix: circular references crashing the sdk

[erunion]

🧰 What's being changed?

This resolves a problem in our handling of API definitions with a circular reference where instead of not leaving them alone, we were dereferencing them. This was causing us to end up with [Circular] JS references that couldn't be stringified into the API definition cache, resulting in a hard crash of api.

Fixes #313

🧬 Testing

See the test I added to cache.test.js.

You can also test this with the definition @josei provided in #313:

const sdk = require('./src')('@codat/v1.1.0#1mld74kq6wk0s1');

sdk
  .ListCompanies()
  .then(res => res.json())
  .then(res => {
    console.log(res);
  })
  .catch(err => {
    console.log(err)
  });

You should see a Response dump with a 401 status code instead of:

RangeError: Maximum call stack size exceeded
    at crawl (/Users/erunion/code/readmeio/api/node_modules/@apidevtools/json-schema-ref-parser/lib/resolve-external.js:54:16)
    at crawl (/Users/erunion/code/readmeio/api/node_modules/@apidevtools/json-schema-ref-parser/lib/resolve-external.js:70:38)
    at crawl (/Users/erunion/code/readmeio/api/node_modules/@apidevtools/json-schema-ref-parser/lib/resolve-external.js:70:38)
    at crawl (/Users/erunion/code/readmeio/api/node_modules/@apidevtools/json-schema-ref-parser/lib/resolve-external.js:70:38)
    at crawl (/Users/erunion/code/readmeio/api/node_modules/@apidevtools/json-schema-ref-parser/lib/resolve-external.js:70:38)
    at crawl (/Users/erunion/code/readmeio/api/node_modules/@apidevtools/json-schema-ref-parser/lib/resolve-external.js:70:38)
    at crawl (/Users/erunion/code/readmeio/api/node_modules/@apidevtools/json-schema-ref-parser/lib/resolve-external.js:70:38)
    at crawl (/Users/erunion/code/readmeio/api/node_modules/@apidevtools/json-schema-ref-parser/lib/resolve-external.js:70:38)
    at crawl (/Users/erunion/code/readmeio/api/node_modules/@apidevtools/json-schema-ref-parser/lib/resolve-external.js:70:38)
    at crawl (/Users/erunion/code/readmeio/api/node_modules/@apidevtools/json-schema-ref-parser/lib/resolve-external.js:70:38)

Note: If running the above code from within packages/api you may ned to clear your definition cache between these two manual tests -- you can do this with rm -rf node_modules/.cache.