switch from python-docutils to ruby-pandoc for rst files

Gemfile

@@ -7,12 +7,12 @@ gem "kramdown", :platforms => :jruby
 gem "RedCloth"
 # using a tag version here because 0.18.3 was not published by the author to encourage users to upgrade.
 # however we want to bump up to this version since this has a security patch
-gem "commonmarker", git: "https://github.com/gjtorikian/commonmarker.git", tag: "v0.18.3"
+gem "commonmarker"
 gem "rdoc", "~>3.6"
 gem "org-ruby", "= 0.9.9"
 gem "creole", "~>0.3.6"
 gem "wikicloth", "=0.8.3"
 gem "twitter-text", "~> 1.14"
 gem "asciidoctor", "~> 2.0.5"
-gem "rake"
+gem "rake", "~> 12.0"
 gem "pandoc-ruby", "= 2.1.10"