fix: support jest.config.json

[zsstiers]

Adds jest.config.json to the list of supported jest.config paths. This list now fully matches the guidance on https://jestjs.io/docs/configuration, which states

It is recommended to define the configuration in a dedicated JavaScript, TypeScript or JSON file. The file will be discovered automatically, if it is named jest.config.js|ts|mjs|cjs|json. You can use --config flag to pass an explicit path to the file.

Fix: #328

[domsleee]

Thanks for your contribution, lgtm 👍