Bump ember-cli from 3.8.2 to 3.9.0 (#321)

Bumps [ember-cli](https://github.com/ember-cli/ember-cli) from 3.8.2 to 3.9.0.
- [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@v3.8.2...v3.9.0)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

package.json

@@ -24,7 +24,7 @@
     "broccoli-asset-rev": "^3.0.0",
     "chai": "^4.1.2",
     "codecov": "^3.3.0",
-    "ember-cli": "~3.8.2",
+    "ember-cli": "~3.9.0",
     "ember-cli-babel": "^7.7.3",
     "ember-cli-dependency-checker": "^3.0.0",
     "ember-cli-htmlbars": "^3.0.0",