Upgrade: Bump sass-loader from 12.6.0 to 13.0.0

Bumps [sass-loader](https://github.com/webpack-contrib/sass-loader) from 12.6.0 to 13.0.0.
- [Release notes](https://github.com/webpack-contrib/sass-loader/releases)
- [Changelog](https://github.com/webpack-contrib/sass-loader/blob/master/CHANGELOG.md)
- [Commits](https://github.com/webpack-contrib/sass-loader/compare/v12.6.0...v13.0.0)

---
updated-dependencies:
- dependency-name: sass-loader
  dependency-type: direct:development
  update-type: version-update:semver-major
...

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

package.json

@@ -17,7 +17,7 @@
     "postcss-loader": "^6.2.1",
     "prettier": "^2.6.2",
     "sass": "^1.51.0",
-    "sass-loader": "^12.6.0",
+    "sass-loader": "^13.0.0",
     "vue-property-decorator": "^9.1.2",
     "vuepress": "^2.0.0-beta.25"
   },