Bump rdoc from 6.5.0 to 6.5.1.1 (#385)

Bumps [rdoc](https://github.com/ruby/rdoc) from 6.5.0 to 6.5.1.1.
- [Release notes](https://github.com/ruby/rdoc/releases)
- [Changelog](https://github.com/ruby/rdoc/blob/master/History.rdoc)
- [Commits](ruby/rdoc@v6.5.0...v6.5.1.1)

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

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

Gemfile.lock

@@ -119,7 +119,7 @@ GEM
       racc
     power_assert (2.0.3)
     profile (0.4.0)
-    psych (4.0.6)
+    psych (5.1.2)
       stringio
     public_suffix (5.0.1)
     racc (1.7.1)
@@ -133,7 +133,7 @@ GEM
       rack (>= 2.1.0)
     rainbow (3.1.1)
     rake (13.0.6)
-    rdoc (6.5.0)
+    rdoc (6.5.1.1)
       psych (>= 4.0.0)
     recursive-open-struct (1.1.3)
     redis (4.4.0)
@@ -185,7 +185,7 @@ GEM
     simplecov-html (0.12.3)
     simplecov_json_formatter (0.1.4)
     slack-notifier (2.4.0)
-    stringio (3.0.2)
+    stringio (3.1.1)
     swd (2.0.2)
       activesupport (>= 3)
       attr_required (>= 0.0.5)