Bump rack from 2.0.6 to 2.0.8

Bumps [rack](https://github.com/rack/rack) from 2.0.6 to 2.0.8.
- [Release notes](https://github.com/rack/rack/releases)
- [Changelog](https://github.com/rack/rack/blob/master/CHANGELOG.md)
- [Commits](rack/rack@2.0.6...2.0.8)

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

Author: dependabot[bot]

Gemfile.lock

@@ -15,7 +15,7 @@ GEM
     minitest (5.11.3)
     multi_json (1.13.1)
     mustermann (1.0.3)
-    rack (2.0.6)
+    rack (2.0.8)
     rack-protection (2.0.4)
       rack
     sinatra (2.0.4)