chore(deps-dev): bump ember-cli-flash from 2.2.0 to 4.0.0

Bumps [ember-cli-flash](https://github.com/adopted-ember-addons/ember-cli-flash) from 2.2.0 to 4.0.0.
- [Release notes](https://github.com/adopted-ember-addons/ember-cli-flash/releases)
- [Changelog](https://github.com/adopted-ember-addons/ember-cli-flash/blob/master/CHANGELOG.md)
- [Commits](adopted-ember-addons/ember-cli-flash@v2.2.0...v4.0.0)

---
updated-dependencies:
- dependency-name: ember-cli-flash
  dependency-type: direct:development
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

package.json

@@ -80,7 +80,7 @@
     "ember-cli-document-title-northm": "^1.0.3",
     "ember-cli-dotenv": "^3.1.0",
     "ember-cli-fastboot": "^4.1.1",
-    "ember-cli-flash": "^2.2.0",
+    "ember-cli-flash": "^4.0.0",
     "ember-cli-head": "^2.0.0",
     "ember-cli-html-minifier": "^1.1.0",
     "ember-cli-htmlbars": "^6.0.1",