Bump rack from 2.0.6 to 2.1.4

Bumps [rack](https://github.com/rack/rack) from 2.0.6 to 2.1.4.
- [Release notes](https://github.com/rack/rack/releases)
- [Changelog](https://github.com/rack/rack/blob/master/CHANGELOG.md)
- [Commits](rack/rack@2.0.6...2.1.4)

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

Author: dependabot[bot]

Gemfile.lock

@@ -11,7 +11,7 @@ GEM
     mime-types-data (3.2018.0812)
     multi_xml (0.6.0)
     mustermann (1.0.3)
-    rack (2.0.6)
+    rack (2.1.4)
     rack-contrib (2.1.0)
       rack (~> 2.0)
     rack-protection (2.0.5)