Bump rdoc from 4.0.1 to 6.3.2

Bumps [rdoc](https://github.com/ruby/rdoc) from 4.0.1 to 6.3.2.
- [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/v4.0.1...v6.3.2)

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

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

Gemfile.lock

@@ -54,7 +54,6 @@ GEM
       nokogiri (= 1.5.10)
       rake
       rdoc
-    json (1.8.1)
     jwt (0.1.8)
       multi_json (>= 1.5)
     kaminari (0.15.0)
@@ -94,8 +93,7 @@ GEM
       rake (>= 0.8.7)
       thor (>= 0.18.1, < 2.0)
     rake (10.1.0)
-    rdoc (4.0.1)
-      json (~> 1.4)
+    rdoc (6.3.2)
     sprockets (2.10.1)
       hike (~> 1.2)
       multi_json (~> 1.0)