Bump rack-protection in /api/ruby/building-a-ci-server (#298)

Bumps [rack-protection](https://github.com/sinatra/sinatra) from 1.5.2 to 1.5.5.
- [Release notes](https://github.com/sinatra/sinatra/releases)
- [Changelog](https://github.com/sinatra/sinatra/blob/master/CHANGELOG.md)
- [Commits](https://github.com/sinatra/sinatra/commits)

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

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

Author: dependabot[bot]

api/ruby/building-a-ci-server/Gemfile.lock

@@ -9,7 +9,7 @@ GEM
     octokit (3.0.0)
       sawyer (~> 0.5.3)
     rack (1.6.13)
-    rack-protection (1.5.2)
+    rack-protection (1.5.5)
       rack
     sawyer (0.5.4)
       addressable (~> 2.3.5)