Bump vue from 2.6.12 to 3.0.0 in /example

Bumps [vue](https://github.com/vuejs/core) from 2.6.12 to 3.0.0.
- [Release notes](https://github.com/vuejs/core/releases)
- [Changelog](https://github.com/vuejs/core/blob/v3.0.0/CHANGELOG.md)
- [Commits](https://github.com/vuejs/core/commits/v3.0.0)

---
updated-dependencies:
- dependency-name: vue
  dependency-version: 3.0.0
  dependency-type: direct:production
...

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Author: dependabot[bot]