chore(deps): [security] bump rack in /tests/apps/ruby

Bumps [rack](https://github.com/rack/rack) from 1.6.11 to 1.6.12. **This update includes a security fix.**
- [Release notes](https://github.com/rack/rack/releases)
- [Changelog](https://github.com/rack/rack/blob/master/CHANGELOG.md)
- [Commits](https://github.com/rack/rack/compare/1.6.11...1.6.12)

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

tests/apps/ruby/Gemfile.lock

@@ -3,7 +3,7 @@ GEM
   specs:
     daemons (1.3.1)
     eventmachine (1.2.7)
-    rack (1.6.11)
+    rack (1.6.12)
     rack-protection (1.5.5)
       rack
     sinatra (1.4.8)