Update to latest Ember and fix tests #116
Description
After the last few PRs, it looks like we're failing in CI against ember-beta and ember-canary. Given that we're also still on Ember 2.8, I think this could be a good opportunity to both get to the bottom of said errors and update the project in general (if anything, to take advantage of Glimmer2 in 2.10 😄). Also, I might try to separate these changes out in that order.