Bump vue-loader from 15.5.1 to 15.6.0 in /apps/updatenotification

Bumps [vue-loader](https://github.com/vuejs/vue-loader) from 15.5.1 to 15.6.0.
- [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/compare/v15.5.1...v15.6.0

)

Signed-off-by: dependabot[bot] <support@dependabot.com>
Signed-off-by: Roeland Jago Douma <roeland@famdouma.nl>