Bump rdoc from 6.7.0 to 6.8.1

Bumps [rdoc](https://github.com/ruby/rdoc) from 6.7.0 to 6.8.1.
- [Release notes](https://github.com/ruby/rdoc/releases)
- [Changelog](https://github.com/ruby/rdoc/blob/master/History.rdoc)
- [Commits](ruby/rdoc@v6.7.0...v6.8.1)

---
updated-dependencies:
- dependency-name: rdoc
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Gemfile

@@ -34,7 +34,7 @@ gem "rack", "~> 3.1"
 gem "rackup", "~> 2.2"
 gem "rack-sanitizer", "~> 2.0"
 gem "rbtrace", "~> 0.5.1"
-gem "rdoc", "~> 6.7"
+gem "rdoc", "~> 6.8"
 gem "roadie-rails", "~> 3.3"
 gem "ruby-magic", "~> 0.6"
 gem "shoryuken", "~> 6.2", require: false

Gemfile.lock

@@ -673,7 +673,7 @@ GEM
       ffi (>= 1.0.6)
       msgpack (>= 0.4.3)
       optimist (>= 3.0.0)
-    rdoc (6.7.0)
+    rdoc (6.8.1)
       psych (>= 4.0.0)
     redcarpet (3.6.0)
     regexp_parser (2.9.2)
@@ -958,7 +958,7 @@ DEPENDENCIES
   rails-i18n (~> 7.0)
   rails_semantic_logger (~> 4.17)
   rbtrace (~> 0.5.1)
-  rdoc (~> 6.7)
+  rdoc (~> 6.8)
   roadie-rails (~> 3.3)
   rotp (~> 6.2)
   rqrcode (~> 2.1)
@@ -1237,7 +1237,7 @@ CHECKSUMS
   rb-fsevent (0.11.2) sha256=43900b972e7301d6570f64b850a5aa67833ee7d87b458ee92805d56b7318aefe
   rb-inotify (0.10.1) sha256=050062d4f31d307cca52c3f6a7f4b946df8de25fc4bd373e1a5142e41034a7ca
   rbtrace (0.5.1) sha256=e8cba64d462bfb8ba102d7be2ecaacc789247d52ac587d8003549d909cb9c5dc
-  rdoc (6.7.0) sha256=b17d5f0f57b0853d7b880d4360a32c7caf8dbb81f8503a36426df809e617f379
+  rdoc (6.8.1) sha256=0128002d1bfc4892bdd780940841e4ca41275f63781fd832d11bc8ba4461462c
   redcarpet (3.6.0) sha256=8ad1889c0355ff4c47174af14edd06d62f45a326da1da6e8a121d59bdcd2e9e9
   regexp_parser (2.9.2) sha256=5a27e767ad634f8a4b544520d5cd28a0db7aa1198a5d7c9d7e11d7b3d9066446
   reline (0.5.11) sha256=868d5f4dbfd9caafa70182f7f6fa258b70baee4e565d7cd9e70b4d5b11a7cb65