Build(deps-dev): Bump ember-cli from 3.9.0 to 3.20.0

Bumps [ember-cli](https://github.com/ember-cli/ember-cli) from 3.9.0 to 3.20.0.
- [Release notes](https://github.com/ember-cli/ember-cli/releases)
- [Changelog](https://github.com/ember-cli/ember-cli/blob/master/CHANGELOG.md)
- [Commits](ember-cli/ember-cli@v3.9.0...v3.20.0)

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

Author: dependabot-preview[bot]

package.json

@@ -51,7 +51,7 @@
     "@types/rsvp": "^4.0.3",
     "@typescript-eslint/eslint-plugin": "^2.8.0",
     "@typescript-eslint/parser": "^2.9.0",
-    "ember-cli": "~3.9.0",
+    "ember-cli": "~3.20.0",
     "ember-cli-dependency-checker": "^3.2.0",
     "ember-cli-htmlbars": "^5.1.0",
     "ember-cli-htmlbars-inline-precompile": "^2.0.0",