Bump rack from 2.0.9 to 2.1.4

Bumps [rack](https://github.com/rack/rack) from 2.0.9 to 2.1.4.
- [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/2.0.9...2.1.4)

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

Gemfile

@@ -48,7 +48,7 @@ gem 'kramdown'
 gem 'liquid'
 gem 'listen'
 gem 'mercenary'
-gem 'rack', '~> 2.0.8'
+gem 'rack', '~> 2.1.4'
 gem 'railties', '>= 5.2.2.1'
 gem 'rouge'
 gem 'rubocop'

Gemfile.lock

@@ -199,7 +199,7 @@ GEM
     pathutil (0.16.2)
       forwardable-extended (~> 2.6)
     public_suffix (4.0.5)
-    rack (2.0.9)
+    rack (2.1.4)
     rack-test (1.1.0)
       rack (>= 1.0, < 3)
     rails-dom-testing (2.0.3)
@@ -300,7 +300,7 @@ DEPENDENCIES
   mini_racer
   minima
   nokogiri (>= 1.10.4)
-  rack (~> 2.0.8)
+  rack (~> 2.1.4)
   railties (>= 5.2.2.1)
   rouge
   rubocop