Bump rack from 2.2.2 to 2.2.3

Bumps [rack](https://github.com/rack/rack) from 2.2.2 to 2.2.3.
- [Release notes](https://github.com/rack/rack/releases)
- [Changelog](https://github.com/rack/rack/blob/master/CHANGELOG.md)
- [Commits](rack/rack@v2.2.2...2.2.3)

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

Author: dependabot[bot]

Gemfile.lock

@@ -5,7 +5,7 @@ GEM
     multi_json (1.14.1)
     mustermann (1.1.1)
       ruby2_keywords (~> 0.0.1)
-    rack (2.2.2)
+    rack (2.2.3)
     rack-protection (2.0.8.1)
       rack
     ruby2_keywords (0.0.2)