Support for ember resolver v5.0.1

[PR 243](https://github.com/ember-cli/ember-resolver/pull/243/files) for ember resolver removed the `DefaultResolver` that this hot loader relied on to properly resolve templates. I spent a good deal of time today trying to reverse engineer how we might otherwise resolve without the `DefaultResolver` but at this time I don't have a solution to write home with. If anyone has time to pitch in and unlock support for `ember-resolver` v5 that would go a long way to helping this project support ember-cli > 3.3