Bump ember-cli from 3.15.1 to 3.15.2

Bumps [ember-cli](https://github.com/ember-cli/ember-cli) from 3.15.1 to 3.15.2.
- [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@v3.15.1...v3.15.2)

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

Author: dependabot-preview[bot]