chore(deps): update dependency kramdown to v2 [security]

Author: renovate-bot

Gemfile

@@ -6,7 +6,7 @@ gem "gems", "~> 1.2"
 gem "google-style", "~> 1.31.0"
 gem "hurley"
 gem "jruby-openssl", platforms: :jruby
-gem "kramdown", "~> 1.5"
+gem "kramdown", "~> 2.3"
 gem "launchy", "~> 2.4"
 gem "rake", "~> 13.0"
 gem "redcarpet", "~> 3.0"