Bump kramdown from 2.2.1 to 2.3.0 in /docs

Bumps [kramdown](https://github.com/gettalong/kramdown) from 2.2.1 to 2.3.0.
- [Release notes](https://github.com/gettalong/kramdown/releases)
- [Changelog](https://github.com/gettalong/kramdown/blob/master/doc/news.page)
- [Commits](https://github.com/gettalong/kramdown/commits)

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

Author: dependabot[bot]

docs/Gemfile.lock

@@ -56,7 +56,7 @@ GEM
       gemoji (~> 3.0)
       html-pipeline (~> 2.2)
       jekyll (>= 3.0, < 5.0)
-    kramdown (2.2.1)
+    kramdown (2.3.0)
       rexml
     kramdown-parser-gfm (1.1.0)
       kramdown (~> 2.0)
@@ -78,7 +78,7 @@ GEM
     rb-fsevent (0.10.4)
     rb-inotify (0.10.1)
       ffi (~> 1.0)
-    rexml (3.2.3)
+    rexml (3.2.4)
     rouge (3.19.0)
     safe_yaml (1.0.5)
     sassc (2.3.0)