When the page is served over an insecure connection, some browsers (Firefox) will disable the
CacheStorage API for security reasons and will throw an error when an attempt is made to use it.
Thus, do not even attempt to use CacheStorage on such connections in the first place.
fix#193
* feat: add support for conditional requests
* feat: add unit tests for conditional requests
* feat: use invariant
* feat: add type guard
* feat: fix lint
* feat: add more unit tests