Bump rack from 2.0.6 to 2.2.2

Bumps [rack](https://github.com/rack/rack) from 2.0.6 to 2.2.2.
- [Release notes](https://github.com/rack/rack/releases)
- [Changelog](https://github.com/rack/rack/blob/master/CHANGELOG.md)
- [Commits](rack/rack@2.0.6...v2.2.2)

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

Author: dependabot[bot]

Gemfile.lock

@@ -58,7 +58,7 @@ GEM
       binding_of_caller (>= 0.7)
       pry (>= 0.9.11)
     psych (3.0.3)
-    rack (2.0.6)
+    rack (2.2.2)
     rake (12.3.2)
     rdoc (6.0.4)
     rspec (3.8.0)