Bump vue-tsc from 2.1.6 to 2.1.8

Bumps [vue-tsc](https://github.com/vuejs/language-tools/tree/HEAD/packages/tsc) from 2.1.6 to 2.1.8.
- [Release notes](https://github.com/vuejs/language-tools/releases)
- [Changelog](https://github.com/vuejs/language-tools/blob/master/CHANGELOG.md)
- [Commits](https://github.com/vuejs/language-tools/commits/v2.1.8/packages/tsc)

---
updated-dependencies:
- dependency-name: vue-tsc
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>