Bump rdoc from 6.6.2 to 6.6.3.1

Bumps [rdoc](https://github.com/ruby/rdoc) from 6.6.2 to 6.6.3.1.
- [Release notes](https://github.com/ruby/rdoc/releases)
- [Changelog](https://github.com/ruby/rdoc/blob/master/History.rdoc)
- [Commits](ruby/rdoc@v6.6.2...v6.6.3.1)

---
updated-dependencies:
- dependency-name: rdoc
  dependency-type: indirect
...

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

Gemfile.lock

@@ -522,7 +522,8 @@ GEM
       css_parser (>= 1.6.0)
       htmlentities (>= 4.0.0)
     promise.rb (0.7.4)
-    psych (5.1.2)
+    psych (5.2.2)
+      date
       stringio
     public_suffix (2.0.5)
     pwqgen.rb (0.1.0)
@@ -594,7 +595,7 @@ GEM
     rdf-xsd (3.2.1)
       rdf (~> 3.2)
       rexml (~> 3.2)
-    rdoc (6.6.2)
+    rdoc (6.6.3.1)
       psych (>= 4.0.0)
     reek (6.3.0)
       dry-schema (~> 1.13.0)
@@ -719,7 +720,7 @@ GEM
       rack (> 1, < 3)
     string_pattern (2.3.0)
       regexp_parser (~> 2.5, >= 2.5.0)
-    stringio (3.1.0)
+    stringio (3.1.2)
     strip_attributes (1.13.0)
       activemodel (>= 3.0, < 8.0)
     sxp (1.2.3)