Bump vue-server-renderer from 2.6.11 to 2.6.12

Bumps [vue-server-renderer](https://github.com/vuejs/vue) from 2.6.11 to 2.6.12.
- [Release notes](https://github.com/vuejs/vue/releases)
- [Commits](https://github.com/vuejs/vue/compare/v2.6.11...v2.6.12

)

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