Bump rack in /api/ruby/building-your-first-github-app

Bumps [rack](https://github.com/rack/rack) from 2.2.6.4 to 2.2.8.1.
- [Release notes](https://github.com/rack/rack/releases)
- [Changelog](https://github.com/rack/rack/blob/main/CHANGELOG.md)
- [Commits](rack/rack@v2.2.6.4...v2.2.8.1)

---
updated-dependencies:
- dependency-name: rack
  dependency-type: indirect
...

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

api/ruby/building-your-first-github-app/Gemfile.lock

@@ -33,7 +33,7 @@ GEM
     octokit (4.9.0)
       sawyer (~> 0.8.0, >= 0.5.3)
     public_suffix (5.0.1)
-    rack (2.2.6.4)
+    rack (2.2.8.1)
     rack-protection (2.2.3)
       rack
     ruby2_keywords (0.0.5)