Module build failed: LoaderRunnerError: Module: '<path>/json-schema-apidoc-loader/lib/loader.js' is not a loader (must have normal or pitch function)

When accessing doca's generated index endpoint, it fails with the error
`Module build failed: LoaderRunnerError: Module: '/json-schema-apidoc-loader/lib/loader.js' is not a loader (must have normal or pitch function)` (already mentioned in #15).

As far as I can tell, the loader definition inside the `config.${ENV}.babel.js` for `json-schema-apidoc-loader` seems to be no longer working because Webpack [changed it's expected format](https://webpack.js.org/concepts/loaders/). Please correct me, if I am wrong - I am no Webpack expert.