Bump rack in /api/ruby/building-your-first-github-app (#310)

Bumps [rack](https://github.com/rack/rack) from 2.0.5 to 2.2.2.
- [Release notes](https://github.com/rack/rack/releases)
- [Changelog](https://github.com/rack/rack/blob/master/CHANGELOG.md)
- [Commits](rack/rack@2.0.5...v2.2.2)

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

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

@@ -11,7 +11,7 @@ GEM
     octokit (4.9.0)
       sawyer (~> 0.8.0, >= 0.5.3)
     public_suffix (3.0.2)
-    rack (2.0.5)
+    rack (2.2.2)
     rack-protection (2.0.3)
       rack
     sawyer (0.8.1)