build(deps-dev): bump vuepress from 1.8.0 to 1.8.1 in /docs (#2318)

Bumps [vuepress](https://github.com/vuejs/vuepress/tree/HEAD/packages/vuepress) from 1.8.0 to 1.8.1.
- [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/v1.8.1/packages/vuepress)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

docs/package.json

@@ -5,7 +5,7 @@
   },
   "devDependencies": {
     "@vuepress/plugin-google-analytics": "^1.8.0",
-    "vuepress": "^1.8.0",
+    "vuepress": "^1.8.1",
     "vuepress-theme-default-prefers-color-scheme": "^1.1.2",
     "vuepress-plugin-sitemap": "^2.3.1"
   }