Upgrade: Bump vuepress from 2.0.0-beta.21 to 2.0.0-beta.23

Bumps [vuepress](https://github.com/vuejs/vuepress/tree/HEAD/packages/vuepress) from 2.0.0-beta.21 to 2.0.0-beta.23.
- [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] <support@github.com>

package.json

@@ -17,7 +17,7 @@
     "sass": "1.35.1",
     "sass-loader": "^12.1.0",
     "vue-property-decorator": "^9.1.2",
-    "vuepress": "^2.0.0-beta.16"
+    "vuepress": "^2.0.0-beta.23"
   },
   "scripts": {
     "docs:dev": "vuepress dev docs",