Update html-pipeline requirement from ~> 2.0 to >= 2, < 4

Updates the requirements on [html-pipeline](https://github.com/gjtorikian/html-pipeline) to permit the latest version.
- [Release notes](https://github.com/gjtorikian/html-pipeline/releases)
- [Changelog](https://github.com/gjtorikian/html-pipeline/blob/main/CHANGELOG.md)
- [Commits](gjtorikian/html-pipeline@v2.0...v2.14.3)

---
updated-dependencies:
- dependency-name: html-pipeline
  dependency-version: 2.14.3
  dependency-type: direct:production
...

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Author: dependabot[bot]

qiita-markdown.gemspec

@@ -20,7 +20,7 @@ Gem::Specification.new do |spec|
   spec.add_dependency "addressable"
   spec.add_dependency "gemoji"
   spec.add_dependency "github-linguist", "~> 7.0"
-  spec.add_dependency "html-pipeline", "~> 2.0"
+  spec.add_dependency "html-pipeline", ">= 2", "< 4"
   spec.add_dependency "mem"
   spec.add_dependency "qiita_marker", "~> 0.23.9"
   spec.add_dependency "rouge", "~> 4.2"