Bump merge and @vue/cli in /web_src

Removes [merge](https://github.com/yeikos/js.merge). It's no longer used after updating ancestor dependency [@vue/cli](https://github.com/vuejs/vue-cli/tree/HEAD/packages/@vue/cli). These dependencies need to be updated together.


Removes `merge`

Updates `@vue/cli` from 4.5.19 to 5.0.8
- [Release notes](https://github.com/vuejs/vue-cli/releases)
- [Changelog](https://github.com/vuejs/vue-cli/blob/dev/CHANGELOG.md)
- [Commits](https://github.com/vuejs/vue-cli/commits/v5.0.8/packages/@vue/cli)

---
updated-dependencies:
- dependency-name: merge
  dependency-type: indirect
- dependency-name: "@vue/cli"
  dependency-type: direct:production
...

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