Dependabot(deps-dev): bump vuepress from 2.0.0-rc.2 to 2.0.0-rc.6

Bumps [vuepress](https://github.com/vuejs/vuepress/tree/HEAD/packages/vuepress) from 2.0.0-rc.2 to 2.0.0-rc.6.
- [Release notes](https://github.com/vuejs/vuepress/releases)
- [Changelog](https://github.com/vuejs/vuepress/blob/master/CHANGELOG.md)
- [Commits](https://github.com/vuejs/vuepress/commits/HEAD/packages/vuepress)

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

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

package.json

@@ -72,7 +72,7 @@
     "vue-loader": "^17.0.1",
     "vue-tsc": "^1.0.24",
     "@vuepress/client": "2.0.0-rc.2",
-    "vuepress": "2.0.0-rc.2",
+    "vuepress": "2.0.0-rc.6",
     "vuepress-plugin-clipboard": "^2.1.4",
     "vuepress-plugin-markdown-checkbox": "^1.0.8"
   },