Merge pull request scala#1975 from scala/dependabot/bundler/kramdown-2.3.1

[Security] Bump kramdown from 2.3.0 to 2.3.1

Author: SethTisue

Gemfile.lock

@@ -45,7 +45,7 @@ GEM
       jekyll (~> 3.0)
     jekyll-watch (2.2.1)
       listen (~> 3.0)
-    kramdown (2.3.0)
+    kramdown (2.3.1)
       rexml
     kramdown-parser-gfm (1.1.0)
       kramdown (~> 2.0)