chore: upgrade kramdown usage to 2.3 per CVE-2020-14001 (#452)

Author: mattwalsh-unity

docs/Gemfile.lock

@@ -23,7 +23,7 @@ GEM
       i18n (~> 0.7)
       jekyll-sass-converter (~> 1.0)
       jekyll-watch (~> 2.0)
-      kramdown (~> 1.14)
+      kramdown (~> 2.3)
       liquid (~> 4.0)
       mercenary (~> 0.3.3)
       pathutil (~> 0.9)
@@ -41,7 +41,7 @@ GEM
       jekyll (>= 3.7, < 5.0)
     jekyll-watch (2.2.1)
       listen (~> 3.0)
-    kramdown (1.17.0)
+    kramdown (2.3.0)
     liquid (4.0.3)
     listen (3.2.1)
       rb-fsevent (~> 0.10, >= 0.10.3)