build: bump ruby-enum from 0.7.2 to 0.8.0 in /docs

Bumps [ruby-enum](https://github.com/dblock/ruby-enum) from 0.7.2 to 0.8.0.
- [Release notes](https://github.com/dblock/ruby-enum/releases)
- [Changelog](https://github.com/dblock/ruby-enum/blob/master/CHANGELOG.md)
- [Commits](https://github.com/dblock/ruby-enum/compare/v0.7.2...v0.8.0

)

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

docs/Gemfile.lock

@@ -229,7 +229,7 @@ GEM
     rb-inotify (0.10.1)
       ffi (~> 1.0)
     rouge (3.13.0)
-    ruby-enum (0.7.2)
+    ruby-enum (0.8.0)
       i18n
     rubyzip (2.3.0)
     safe_yaml (1.0.5)