Bump rdoc from 6.12.0 to 6.13.0

Bumps [rdoc](https://github.com/ruby/rdoc) from 6.12.0 to 6.13.0.
- [Release notes](https://github.com/ruby/rdoc/releases)
- [Changelog](https://github.com/ruby/rdoc/blob/master/History.rdoc)
- [Commits](https://github.com/ruby/rdoc/compare/v6.12.0...v6.13.0)

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

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

Gemfile

@@ -63,7 +63,7 @@ end
 group :test do
     gem 'test-unit-full', '~> 0.0.5'
     gem 'rspec', '~> 3.13'
-    gem 'rdoc', '~> 6.12'
+    gem 'rdoc', '~> 6.13'
     gem 'browserstack-local', '~> 1.4'
 
     gem 'irb', '~> 1.15'

Gemfile.lock

@@ -147,7 +147,7 @@ GEM
       rack (>= 1.3)
     rainbow (3.1.1)
     rake (13.2.1)
-    rdoc (6.12.0)
+    rdoc (6.13.0)
       psych (>= 4.0.0)
     regexp_parser (2.10.0)
     reline (0.6.0)
@@ -207,7 +207,7 @@ GEM
       tilt (~> 2.0)
     slack-notifier (2.4.0)
     sqlite3 (2.6.0-x86_64-linux-gnu)
-    stringio (3.1.2)
+    stringio (3.1.6)
     sync (0.5.0)
     term-ansicolor (1.11.2)
       tins (~> 1.0)
@@ -285,7 +285,7 @@ DEPENDENCIES
   rack (~> 2.2)
   rack-protection (~> 3.2.0)
   rake (~> 13.2)
-  rdoc (~> 6.12)
+  rdoc (~> 6.13)
   rest-client (~> 2.1.0)
   rspec (~> 3.13)
   rubocop (~> 1.75.1)