Bump kramdown from 2.1.0 to 2.3.0

Bumps [kramdown](https://github.com/gettalong/kramdown) from 2.1.0 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

@@ -8,7 +8,9 @@ GEM
     em-websocket (0.5.1)
       eventmachine (>= 0.12.9)
       http_parser.rb (~> 0.6.0)
+    eventmachine (1.2.7)
     eventmachine (1.2.7-x64-mingw32)
+    ffi (1.11.3)
     ffi (1.11.3-x64-mingw32)
     forwardable-extended (2.6.0)
     http_parser.rb (0.6.0)
@@ -39,7 +41,8 @@ GEM
       jekyll (>= 3.7, < 5.0)
     jekyll-watch (2.2.1)
       listen (~> 3.0)
-    kramdown (2.1.0)
+    kramdown (2.3.0)
+      rexml
     kramdown-parser-gfm (1.1.0)
       kramdown (~> 2.0)
     liquid (4.0.3)
@@ -57,8 +60,11 @@ GEM
     rb-fsevent (0.10.3)
     rb-inotify (0.10.1)
       ffi (~> 1.0)
+    rexml (3.2.4)
     rouge (3.15.0)
     safe_yaml (1.0.5)
+    sassc (2.2.1)
+      ffi (~> 1.9)
     sassc (2.2.1-x64-mingw32)
       ffi (~> 1.9)
     terminal-table (1.8.0)
@@ -72,6 +78,7 @@ GEM
     wdm (0.1.1)
 
 PLATFORMS
+  ruby
   x64-mingw32
 
 DEPENDENCIES