fix: update rdoc requirement from 6.3.2 to 6.5.0

Updates the requirements on [rdoc](https://github.com/ruby/rdoc) to permit the latest version.
- [Release notes](https://github.com/ruby/rdoc/releases)
- [Changelog](https://github.com/ruby/rdoc/blob/master/History.rdoc)
- [Commits](ruby/rdoc@v6.3.2...v6.5.0)

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

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

Gemfile

@@ -6,6 +6,6 @@ gem "asciidoctor", "2.0.16"
 gem "commonmarker", "=0.21.0"
 gem "creole", "=0.5.0"
 gem "org-ruby", "=0.9.12"
-gem "rdoc", "6.3.2"
+gem "rdoc", "6.5.0"
 gem "redcarpet", "3.6.0"
 gem "wikicloth", "=0.8.3"