Bump rack from 2.2.8 to 2.2.8.1 (#359)

Bumps [rack](https://github.com/rack/rack) from 2.2.8 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@v2.2.8...v2.2.8.1)

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

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Gemfile.lock

@@ -10,7 +10,7 @@ GEM
     maruku (0.7.3)
     mustermann (3.0.0)
       ruby2_keywords (~> 0.0.1)
-    rack (2.2.8)
+    rack (2.2.8.1)
     rack-protection (3.2.0)
       base64 (>= 0.1.0)
       rack (~> 2.2, >= 2.2.4)