[Security] Bump rack from 2.0.5 to 2.0.6

Bumps [rack](https://github.com/rack/rack) from 2.0.5 to 2.0.6. **This update includes security fixes.**
- [Release notes](https://github.com/rack/rack/releases)
- [Changelog](https://github.com/rack/rack/blob/master/CHANGELOG.md)
- [Commits](rack/rack@2.0.5...2.0.6)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot-support

Gemfile.lock

@@ -42,7 +42,7 @@ GEM
       method_source (~> 0.8.1)
       slop (~> 3.4)
     public_suffix (2.0.5)
-    rack (2.0.5)
+    rack (2.0.6)
     rack-protection (2.0.2)
       rack
     rake (11.2.2)