Bump vue-loader from 15.6.0 to 15.6.2 in /apps/oauth2

Bumps [vue-loader](https://github.com/vuejs/vue-loader) from 15.6.0 to 15.6.2.
- [Release notes](https://github.com/vuejs/vue-loader/releases)
- [Changelog](https://github.com/vuejs/vue-loader/blob/master/CHANGELOG.md)
- [Commits](https://github.com/vuejs/vue-loader/commits

)

Signed-off-by: dependabot[bot] <support@dependabot.com>
Signed-off-by: Christoph Wurst <christoph@winzerhof-wurst.at>