Update rouge requirement from ~> 3 to ~> 4 in /.docker/entrypoint

Updates the requirements on [rouge](https://github.com/rouge-ruby/rouge) to permit the latest version.
- [Release notes](https://github.com/rouge-ruby/rouge/releases)
- [Changelog](https://github.com/rouge-ruby/rouge/blob/master/CHANGELOG.md)
- [Commits](rouge-ruby/rouge@v3.0.0...v4.0.0)

---
updated-dependencies:
- dependency-name: rouge
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

.docker/entrypoint/Gemfile

@@ -9,7 +9,7 @@ gem 'jekyll', '~> 4'
 gem 'jekyll-material-icon-tag', '~> 1.0'
 gem 'jemoji', '>= 0.12'
 gem 'kramdown-plantuml', '>= 1.1.12'
-gem 'rouge', '~> 3'
+gem 'rouge', '~> 4'
 
 group :development, :test do
   gem 'codecov', '>= 0.6'