Bump rdoc from 6.14.2 to 6.15.0

Bumps [rdoc](https://github.com/ruby/rdoc) from 6.14.2 to 6.15.0.
- [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/v6.14.2...v6.15.0)

---
updated-dependencies:
- dependency-name: rdoc
  dependency-version: 6.15.0
  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', '~> 6.14'
+    gem 'rdoc', '~> 6.15'
     gem 'browserstack-local', '~> 1.4'
 
     gem 'irb', '~> 1.15'

Gemfile.lock

@@ -62,7 +62,7 @@ GEM
     em-websocket (0.5.3)
       eventmachine (>= 0.12.9)
       http_parser.rb (~> 0)
-    erb (5.0.2)
+    erb (5.0.3)
     erubis (2.7.0)
     espeak-ruby (1.1.0)
     event_emitter (0.2.6)
@@ -166,9 +166,10 @@ GEM
       rack (>= 1.3)
     rainbow (3.1.1)
     rake (13.3.0)
-    rdoc (6.14.2)
+    rdoc (6.15.0)
       erb
       psych (>= 4.0.0)
+      tsort
     regexp_parser (2.11.3)
     reline (0.6.2)
       io-console (~> 0.5)
@@ -268,6 +269,7 @@ GEM
     tins (1.43.0)
       bigdecimal
       sync
+    tsort (0.2.0)
     tzinfo (2.0.6)
       concurrent-ruby (~> 1.0)
     uglifier (4.2.1)
@@ -322,7 +324,7 @@ DEPENDENCIES
   rack (~> 3.2)
   rack-protection (~> 4.1.1)
   rake (~> 13.3)
-  rdoc (~> 6.14)
+  rdoc (~> 6.15)
   rest-client (~> 2.1.0)
   rspec (~> 3.13)
   rubocop (~> 1.81.1)