chore: Bump rack from 3.1.7 to 3.1.8 (#895)

Bumps [rack](https://github.com/rack/rack) from 3.1.7 to 3.1.8.
- [Release notes](https://github.com/rack/rack/releases)
- [Changelog](https://github.com/rack/rack/blob/main/CHANGELOG.md)
- [Commits](https://github.com/rack/rack/compare/v3.1.7...v3.1.8)

---
updated-dependencies:
- dependency-name: rack
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Gemfile

@@ -33,7 +33,7 @@ gem 'kramdown'
 gem 'liquid'
 gem 'listen'
 gem 'mercenary'
-gem 'rack', '~> 3.1.7'
+gem 'rack', '~> 3.1.8'
 gem 'railties', '>= 5.2.2.1'
 gem 'rouge'
 gem 'rubocop'

Gemfile.lock

@@ -225,7 +225,7 @@ GEM
       stringio
     public_suffix (6.0.1)
     racc (1.8.1)
-    rack (3.1.7)
+    rack (3.1.8)
     rack-session (2.0.0)
       rack (>= 3.0.0)
     rack-test (2.1.0)
@@ -340,7 +340,7 @@ DEPENDENCIES
   mini_racer (~> 0.15.0)
   minima!
   nokogiri (>= 1.10.4)
-  rack (~> 3.1.7)
+  rack (~> 3.1.8)
   railties (>= 5.2.2.1)
   rouge
   rubocop