Bump core-js from 2.6.8 to 2.6.9
Bump core-js from 2.6.8 to 2.6.9

Bumps [core-js](https://github.com/zloirock/core-js) from 2.6.8 to 2.6.9.
- [Release notes](https://github.com/zloirock/core-js/releases)
- [Changelog](https://github.com/zloirock/core-js/blob/master/CHANGELOG.md)
- [Commits](https://github.com/zloirock/core-js/compare/v2.6.8...v2.6.9)
sue445/chrome-gitlab-notifier,sue445/chrome-gitlab-notifier