Bump rdoc from 4.2.2 to 6.0.4

Bumps [rdoc](https://github.com/ruby/rdoc) from 4.2.2 to 6.0.4.
- [Release notes](https://github.com/ruby/rdoc/releases)
- [Changelog](https://github.com/ruby/rdoc/blob/master/History.rdoc)
- [Commits](https://github.com/ruby/rdoc/commits)

Signed-off-by: dependabot[bot] <support@dependabot.com>

Author: dependabot-support

Gemfile

@@ -141,7 +141,7 @@ gem 'gitlab-markup', '~> 1.6.2'
 gem 'redcarpet', '~> 3.4'
 gem 'commonmarker', '~> 0.17'
 gem 'RedCloth', '~> 4.3.2'
-gem 'rdoc', '~> 4.2'
+gem 'rdoc', '~> 6.0'
 gem 'org-ruby', '~> 0.9.12'
 gem 'creole', '~> 0.5.0'
 gem 'wikicloth', '0.8.1'

Gemfile.lock

@@ -707,8 +707,7 @@ GEM
       ffi
     rbnacl-libsodium (1.0.11)
       rbnacl (>= 3.0.1)
-    rdoc (4.2.2)
-      json (~> 1.4)
+    rdoc (6.0.4)
     re2 (1.1.1)
     recaptcha (3.0.0)
       json
@@ -1151,7 +1150,7 @@ DEPENDENCIES
   rblineprof (~> 0.3.6)
   rbnacl (~> 4.0)
   rbnacl-libsodium
-  rdoc (~> 4.2)
+  rdoc (~> 6.0)
   re2 (~> 1.1.1)
   recaptcha (~> 3.0)
   redcarpet (~> 3.4)