EmberCLI 3.5 causes dependency resolution problems

[rondale-sc]

When running this with EmberCLI 3.5 (assuming the broccoli 2 changes are the culprit) rollup has trouble finding external dependencies even when it should be able to find them.

[locks]

@rondale-sc still happening?

[rwjblue]

@locks - ya, but I believe that its only when running this repo and that normal glimmer.js apps work fine with ember-cli@3.5+