Bump rack from 1.6.11 to 2.2.3

Bumps [rack](https://github.com/rack/rack) from 1.6.11 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@1.6.11...2.2.3)

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

Author: dependabot[bot]

Gemfile.lock

@@ -53,7 +53,7 @@ GEM
     multi_json (1.3.4)
     nokogiri (1.10.4)
       mini_portile2 (~> 2.4.0)
-    rack (1.6.11)
+    rack (2.2.3)
     rack-test (0.6.1)
       rack (>= 1.0)
     rake (0.9.2.2)