Bump kramdown from 1.13.2 to 2.3.0

Bumps [kramdown](https://github.com/gettalong/kramdown) from 1.13.2 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>

Gemfile.lock

@@ -168,7 +168,8 @@ GEM
       oauth2 (~> 1.4)
       ox (~> 2.1)
       uri_template (~> 0.7.0)
-    kramdown (1.13.2)
+    kramdown (2.3.0)
+      rexml
     listen (3.1.5)
       rb-fsevent (~> 0.9, >= 0.9.4)
       rb-inotify (~> 0.9, >= 0.9.7)
@@ -243,6 +244,7 @@ GEM
       ffi (>= 0.5.0)
     representable (2.3.0)
       uber (~> 0.0.7)
+    rexml (3.2.4)
     roar (1.0.4)
       representable (>= 2.0.1, < 2.4.0)
     role_playing (0.1.5)