Bump kramdown from 2.3.0 to 2.3.1

Bumps [kramdown](https://github.com/gettalong/kramdown) from 2.3.0 to 2.3.1.
- [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] <[email protected]>

Author: dependabot[bot]

Gemfile.lock

@@ -192,7 +192,7 @@ GEM
       activerecord
       kaminari-core (= 1.2.1)
     kaminari-core (1.2.1)
-    kramdown (2.3.0)
+    kramdown (2.3.1)
       rexml
     listen (3.4.1)
       rb-fsevent (~> 0.10, >= 0.10.3)