Update pygments.rb requirement from 3.0.0 to 4.0.0 (#83)

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

---
updated-dependencies:
- dependency-name: pygments.rb
  dependency-version: 4.0.0
  dependency-type: direct:production
...

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

Author: dependabot[bot]

Gemfile

@@ -11,7 +11,7 @@ gem 'asciidoctor-epub3', '2.2.0'
 gem 'asciidoctor-pdf', '2.3.19'
 
 gem 'coderay', '1.1.3'
-gem 'pygments.rb', '3.0.0'
+gem 'pygments.rb', '4.0.0'
 gem 'thread_safe', '0.3.6'
 gem 'epubcheck-ruby', '5.2.1.0'
 gem 'html-proofer', '5.0.10'