App won't build with ember-exam 6.1.0 and ember-mocha

```
Build Error (Bundler)

ember-exam tried to import "ember-qunit" but the package was not resolvable from {directories}/node_modules/ember-exam

Stack Trace and Error Report: /var/folders/qf/lrfvnjyn57bf8fs0g908c0p40000gn/T/error.dump.5fcdb4584b886598cb025504493336b4.log
```

Steps to reproduce:
- Create new ember app from scratch
- Install `ember-exam` and `ember-mocha`
- Uninstall `ember-qunit`
- Start app

The log as well just in case it's desired:
```
ERROR Summary:

- broccoliBuilderErrorStack: Error: ember-exam tried to import "ember-qunit" but the package was not resolvable from /Users/rbaxter/gg/client/src/greenlight/node_modules/ember-exam
at Package.resolve (/Users/rbaxter/gg/client/src/greenlight/node_modules/ember-auto-import/js/package.js:163:19)
at Splitter. (/Users/rbaxter/gg/client/src/greenlight/node_modules/ember-auto-import/js/splitter.js:76:38)
at Generator.next ()
at /Users/rbaxter/gg/client/src/greenlight/node_modules/ember-auto-import/js/splitter.js:8:71
at new Promise ()
at __awaiter (/Users/rbaxter/gg/client/src/greenlight/node_modules/ember-auto-import/js/splitter.js:4:12)
at Splitter.handleLiteralImport (/Users/rbaxter/gg/client/src/greenlight/node_modules/ember-auto-import/js/splitter.js:75:16)
at Splitter. (/Users/rbaxter/gg/client/src/greenlight/node_modules/ember-auto-import/js/splitter.js:65:32)
at Generator.next ()
at /Users/rbaxter/gg/client/src/greenlight/node_modules/ember-auto-import/js/splitter.js:8:71
- code: [undefined]
- codeFrame: ember-exam tried to import "ember-qunit" but the package was not resolvable from /Users/rbaxter/gg/client/src/greenlight/node_modules/ember-exam
- errorMessage: ember-exam tried to import "ember-qunit" but the package was not resolvable from /Users/rbaxter/gg/client/src/greenlight/node_modules/ember-exam
at Bundler
-~- created here: -~-
at new Plugin (/Users/rbaxter/gg/client/src/greenlight/node_modules/ember-auto-import/node_modules/broccoli-plugin/dist/index.js:47:36)
at new Bundler (/Users/rbaxter/gg/client/src/greenlight/node_modules/ember-auto-import/js/bundler.js:34:9)
at AutoImport.makeBundler (/Users/rbaxter/gg/client/src/greenlight/node_modules/ember-auto-import/js/auto-import.js:57:16)
at AutoImport.addTo (/Users/rbaxter/gg/client/src/greenlight/node_modules/ember-auto-import/js/auto-import.js:67:38)
at EmberApp.host.addonPostprocessTree (/Users/rbaxter/gg/client/src/greenlight/node_modules/ember-auto-import/js/auto-import.js:101:29)
at EmberApp.toTree (/Users/rbaxter/gg/client/src/greenlight/node_modules/ember-cli/lib/broccoli/ember-app.js:1665:17)
at EmberApp.appInstance.toTree (/Users/rbaxter/gg/client/src/greenlight/node_modules/ember-classic-decorator/node_modules/@embroider/macros/src/ember-addon-main.js:48:35)
at EmberApp.appInstance.toTree (/Users/rbaxter/gg/client/src/greenlight/node_modules/ember-cli-mirage/node_modules/@embroider/macros/src/ember-addon-main.js:48:35)
at EmberApp.appInstance.toTree (/Users/rbaxter/gg/client/src/greenlight/node_modules/ember-exam/node_modules/@embroider/macros/src/ember-addon-main.js:48:35)
at EmberApp.appInstance.toTree (/Users/rbaxter/gg/client/src/greenlight/node_modules/ember-basic-dropdown/node_modules/@embroider/macros/src/ember-addon-main.js:48:35)
-~- (end) -~-
- errorType: Build Error
- location:
- column: [undefined]
- file: [undefined]
- line: [undefined]
- treeDir: [undefined]
- message: ember-exam tried to import "ember-qunit" but the package was not resolvable from /Users/rbaxter/gg/client/src/greenlight/node_modules/ember-exam
at Bundler
-~- created here: -~-
at new Plugin (/Users/rbaxter/gg/client/src/greenlight/node_modules/ember-auto-import/node_modules/broccoli-plugin/dist/index.js:47:36)
at new Bundler (/Users/rbaxter/gg/client/src/greenlight/node_modules/ember-auto-import/js/bundler.js:34:9)
at AutoImport.makeBundler (/Users/rbaxter/gg/client/src/greenlight/node_modules/ember-auto-import/js/auto-import.js:57:16)
at AutoImport.addTo (/Users/rbaxter/gg/client/src/greenlight/node_modules/ember-auto-import/js/auto-import.js:67:38)
at EmberApp.host.addonPostprocessTree (/Users/rbaxter/gg/client/src/greenlight/node_modules/ember-auto-import/js/auto-import.js:101:29)
at EmberApp.toTree (/Users/rbaxter/gg/client/src/greenlight/node_modules/ember-cli/lib/broccoli/ember-app.js:1665:17)
at EmberApp.appInstance.toTree (/Users/rbaxter/gg/client/src/greenlight/node_modules/ember-classic-decorator/node_modules/@embroider/macros/src/ember-addon-main.js:48:35)
at EmberApp.appInstance.toTree (/Users/rbaxter/gg/client/src/greenlight/node_modules/ember-cli-mirage/node_modules/@embroider/macros/src/ember-addon-main.js:48:35)
at EmberApp.appInstance.toTree (/Users/rbaxter/gg/client/src/greenlight/node_modules/ember-exam/node_modules/@embroider/macros/src/ember-addon-main.js:48:35)
at EmberApp.appInstance.toTree (/Users/rbaxter/gg/client/src/greenlight/node_modules/ember-basic-dropdown/node_modules/@embroider/macros/src/ember-addon-main.js:48:35)
-~- (end) -~-
- name: Error
- nodeAnnotation: [undefined]
- nodeName: Bundler
- originalErrorMessage: ember-exam tried to import "ember-qunit" but the package was not resolvable from /Users/rbaxter/gg/client/src/greenlight/node_modules/ember-exam
- stack: Error: ember-exam tried to import "ember-qunit" but the package was not resolvable from /Users/rbaxter/gg/client/src/greenlight/node_modules/ember-exam
at Package.resolve (/Users/rbaxter/gg/client/src/greenlight/node_modules/ember-auto-import/js/package.js:163:19)
at Splitter. (/Users/rbaxter/gg/client/src/greenlight/node_modules/ember-auto-import/js/splitter.js:76:38)
at Generator.next ()
at /Users/rbaxter/gg/client/src/greenlight/node_modules/ember-auto-import/js/splitter.js:8:71
at new Promise ()
at __awaiter (/Users/rbaxter/gg/client/src/greenlight/node_modules/ember-auto-import/js/splitter.js:4:12)
at Splitter.handleLiteralImport (/Users/rbaxter/gg/client/src/greenlight/node_modules/ember-auto-import/js/splitter.js:75:16)
at Splitter. (/Users/rbaxter/gg/client/src/greenlight/node_modules/ember-auto-import/js/splitter.js:65:32)
at Generator.next ()
at /Users/rbaxter/gg/client/src/greenlight/node_modules/ember-auto-import/js/splitter.js:8:71

=================================================================================

```