Bump ember-cli from 3.14.0 to 3.15.0

Bumps [ember-cli](https://github.com/ember-cli/ember-cli) from 3.14.0 to 3.15.0.
- [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@v3.14.0...v3.15.0)

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

Author: dependabot-preview[bot]

package-lock.json

@@ -34,7 +34,7 @@
     "broccoli-asset-rev": "^3.0.0",
     "ember-a11y-testing": "^2.0.0",
     "ember-auto-import": "^1.5.3",
-    "ember-cli": "~3.14.0",
+    "ember-cli": "~3.15.0",
     "ember-cli-app-version": "^3.1.3",
     "ember-cli-babel": "^7.13.2",
     "ember-cli-clipboard": "^0.9.0",