build(deps-dev): bump posthtml-markdownit from 2.0.0 to 3.1.0

Bumps [posthtml-markdownit](https://github.com/posthtml/posthtml-markdownit) from 2.0.0 to 3.1.0.
- [Release notes](https://github.com/posthtml/posthtml-markdownit/releases)
- [Commits](posthtml/posthtml-markdownit@v2.0.0...v3.1.0)

---
updated-dependencies:
- dependency-name: posthtml-markdownit
  dependency-type: direct:development
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

package-lock.json

@@ -46,7 +46,7 @@
     "markdown-it-toc-done-right": "^4.2.0",
     "posthtml-beautify": "^0.7.0",
     "posthtml-include": "^1.7.4",
-    "posthtml-markdownit": "^2.0.0",
+    "posthtml-markdownit": "^3.1.0",
     "xo": "^0.37.1"
   }
 }