Bumps [vue-loader](https://github.com/vuejs/vue-loader) from 15.9.3 to 15.9.4.
- [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/v15.9.3...v15.9.4

)

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