The `fetch-with-cache` utility was failing to actually cache anything.
It would cache an object with cache time and URL, and would return that
instead of a valid response. This resulted in the error:
`TypeError: fourByteResponse.json is not a function`
The utility was updated to call `.json()` within itself, and cache the
JSON response. The function signature was updated as well, to expect an
options object instead of just the `cacheRefreshTime` option. The
timeout was added to this options object, which helped with testing.
The utility method now also handles unsuccessfull responses, and
incompatible `fetch` options.
Mark Stacey