Bump rack from 2.1.4 to 2.2.3

Bumps [rack](https://github.com/rack/rack) from 2.1.4 to 2.2.3.
- [Release notes](https://github.com/rack/rack/releases)
- [Changelog](https://github.com/rack/rack/blob/master/CHANGELOG.md)
- [Commits](https://github.com/rack/rack/compare/2.1.4...2.2.3)

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

Gemfile

@@ -34,7 +34,7 @@ gem 'kramdown'
 gem 'liquid'
 gem 'listen'
 gem 'mercenary'
-gem 'rack', '~> 2.1.4'
+gem 'rack', '~> 2.2.3'
 gem 'railties', '>= 5.2.2.1'
 gem 'rouge'
 gem 'rubocop'

Gemfile.lock

@@ -168,7 +168,7 @@ GEM
     pathutil (0.16.2)
       forwardable-extended (~> 2.6)
     public_suffix (4.0.5)
-    rack (2.1.4)
+    rack (2.2.3)
     rack-test (1.1.0)
       rack (>= 1.0, < 3)
     rails-dom-testing (2.0.3)
@@ -257,7 +257,7 @@ DEPENDENCIES
   mini_racer
   minima
   nokogiri (>= 1.10.4)
-  rack (~> 2.1.4)
+  rack (~> 2.2.3)
   railties (>= 5.2.2.1)
   rouge
   rubocop