build(deps): bump rouge from 3.19.0 to 3.21.0 in /docs/v3

Bumps [rouge](https://github.com/rouge-ruby/rouge) from 3.19.0 to 3.21.0.
- [Release notes](https://github.com/rouge-ruby/rouge/releases)
- [Changelog](https://github.com/rouge-ruby/rouge/blob/master/CHANGELOG.md)
- [Commits](rouge-ruby/rouge@v3.19.0...v3.21.0)

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

Author: dependabot[bot]

docs/v3/Gemfile.lock

@@ -118,7 +118,7 @@ GEM
     rb-inotify (0.10.1)
       ffi (~> 1.0)
     redcarpet (3.5.0)
-    rouge (1.10.1)
+    rouge (1.11.1)
     sass (3.4.25)
     sprockets (2.12.5)
       hike (~> 1.2)