diff --git a/Dockerfile b/Dockerfile
index 0d511180..e544ff13 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,38 +1,67 @@
-FROM ubuntu:trusty
+FROM ubuntu:focal
 
 RUN apt-get update -qq
-RUN apt-get install -y apt-transport-https
+RUN apt-get install -y \
+    apt-transport-https \
+    locales \
+    software-properties-common \
+    curl \
+    gnupg2
 
-RUN apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv 379CE192D401AB61
-RUN echo "deb https://dl.bintray.com/nxadm/rakudo-pkg-debs `lsb_release -cs` main" | tee -a /etc/apt/sources.list.d/rakudo-pkg.list
+# add the Raku repository
+RUN curl -1sLf 'https://dl.cloudsmith.io/public/nxadm-pkgs/rakudo-pkg/gpg.0DD4CA7EB1C6CC6B.key' |  gpg --dearmor >> /usr/share/keyrings/nxadm-pkgs-rakudo-pkg-archive-keyring.gpg
+RUN curl -1sLf 'https://dl.cloudsmith.io/public/nxadm-pkgs/rakudo-pkg/config.deb.txt?distro=ubuntu&codename=focal&component=main' > /etc/apt/sources.list.d/nxadm-pkgs-rakudo-pkg.list
+# add the Node.js repository
+RUN curl -1sLf https://deb.nodesource.com/setup_20.x | bash
 RUN apt-get update -qq
 
 RUN apt-get install -y \
-    perl rakudo-pkg curl git build-essential \
-    libssl-dev libreadline-dev zlib1g-dev \
-    libicu-dev cmake pkg-config
+    perl \
+    rakudo-pkg \
+    git \
+    libssl-dev \
+    libreadline-dev \
+    zlib1g-dev \
+    libicu-dev \
+    cmake \
+    build-essential \
+    g++ \
+    pkg-config \
+    nodejs \
+    libffi-dev \
+    libyaml-dev \
+    gcc \
+    libxslt-dev \
+    libxml2-dev \
+    zlib1g-dev \
+    libidn11-dev
 
 ENV PATH $PATH:/opt/rakudo-pkg/bin
-RUN install-zef-as-user && zef install Pod::To::HTML
+RUN install-zef
+ENV PATH $PATH:/root/.raku/bin
+RUN zef install Pod::To::HTML2
 
 RUN curl -L http://cpanmin.us | perl - App::cpanminus
 RUN cpanm --installdeps --notest Pod::Simple
 
+# Install Rbenv and Ruby
+RUN git clone https://github.com/rbenv/rbenv.git ~/.rbenv && echo 'export PATH="$HOME/.rbenv/bin:$PATH"' >> ~/.bashrc && echo 'eval "$(rbenv init -)"' >> ~/.bashrc
+RUN git clone https://github.com/rbenv/ruby-build.git ~/.rbenv/plugins/ruby-build
 ENV PATH $PATH:/root/.rbenv/bin:/root/.rbenv/shims
-RUN curl -fsSL https://github.com/rbenv/rbenv-installer/raw/master/bin/rbenv-installer | bash
-RUN rbenv install 2.4.1
-RUN rbenv global 2.4.1
-RUN rbenv rehash
+RUN cd /root/.rbenv/plugins/ruby-build && git pull && cd -
+ENV RUBY_VERSION 3.3.0
+RUN rbenv install $RUBY_VERSION && rbenv global $RUBY_VERSION && rbenv rehash
+RUN echo 'gem: --no-rdoc --no-ri' >> /.gemrc
+RUN gem install bundler:2.4.22
 
-RUN gem install bundler
+RUN bundle config --global build.nokogiri --use-system-libraries
 
 RUN dpkg -i https://github.com/jgm/pandoc/releases/download/3.1.12.1/pandoc-3.1.12.1-linux-amd64.tar.gz
 
 WORKDIR /data/github-markup
 COPY github-markup.gemspec .
 COPY Gemfile .
-COPY Gemfile.lock .
-COPY lib/github-markup.rb lib/github-markup.rb
+ADD lib ./lib
 RUN bundle
 
 ENV LC_ALL en_US.UTF-8
diff --git a/Gemfile b/Gemfile
index a6982244..0e1aa030 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,18 +1,19 @@
 source "http://rubygems.org"
 gemspec
 
+gem "nokogiri", force_ruby_platform: true
 gem "posix-spawn", :platforms => :ruby
 gem "redcarpet", :platforms => :ruby
 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"
-gem "rdoc", "~>3.6"
-gem "org-ruby", "= 0.9.9"
-gem "creole", "~>0.3.6"
+gem "commonmarker", "= 1.0.4"
+gem 'rdoc', '~> 6.6', '>= 6.6.2'
+gem 'org-ruby', '~> 0.9.12'
+gem 'creole', '~> 0.5.0'
+gem 'idn-ruby', '~> 0.1.5'
+gem 'twitter-text', '~> 3.1'
 gem "wikicloth", "=0.8.3"
-gem "twitter-text", "~> 1.14"
-gem "asciidoctor", "~> 2.0.5"
-gem "rake", "~> 12"
-gem "pandoc-ruby", "= 2.1.10"
+gem 'asciidoctor', '~> 2.0', '>= 2.0.21'
+gem 'rake', '~> 13.1'
+gem 'pandoc-ruby', '~> 2.1', '>= 2.1.10'
+
diff --git a/github-markup.gemspec b/github-markup.gemspec
index 594d3507..e4da71d2 100644
--- a/github-markup.gemspec
+++ b/github-markup.gemspec
@@ -1,30 +1,38 @@
-require File.expand_path("../lib/github-markup", __FILE__)
-
-Gem::Specification.new do |s|
-  s.name          = "github-markup"
-  s.version       = GitHub::Markup::VERSION
-  s.summary       = "The code GitHub uses to render README.markup"
-  s.description   = <<~DESC
-    This gem is used by GitHub to render any fancy markup such as Markdown,
-    Textile, Org-Mode, etc. Fork it and add your own!
-  DESC
-  s.authors       = ["Chris Wanstrath"]
-  s.email         = "chris@ozmm.org"
-  s.homepage      = "https://github.com/github/markup"
-  s.license       = "MIT"
-
-  s.files         = `git ls-files`.split($\)
-  s.files        += Dir['vendor/**/*']
-  s.executables   = s.files.grep(%r{^bin/}).map{ |f| File.basename(f) }
-  s.test_files    = s.files.grep(%r{^(test|spec|features)/})
-  s.require_paths = %w[lib]
-
-  s.add_development_dependency 'rake', '~> 12'
-  s.add_development_dependency 'activesupport', '~> 4.0'
-  s.add_development_dependency 'minitest', '~> 5.4', '>= 5.4.3'
-  s.add_development_dependency 'html-pipeline', '~> 1.0'
-  s.add_development_dependency 'sanitize', '>= 4.6.3'
-  s.add_development_dependency 'nokogiri', '~> 1.8.1'
-  s.add_development_dependency 'nokogiri-diff', '~> 0.2.0'
-  s.add_development_dependency "github-linguist", ">= 7.1.3"
-end
+# frozen_string_literal: true
+
+require_relative "lib/github/markup/version"
+
+Gem::Specification.new do |spec|
+  spec.name        = "github-markup"
+  spec.version     = GitHub::Markup::VERSION
+  spec.homepage    = "https://github.com/github/markup"
+  spec.summary     = "The code GitHub uses to render README.markup"
+  spec.description = <<~DESC
+  This gem is used by GitHub to render any fancy markup such as Markdown,
+  Textile, Org-Mode, etc. Fork it and add your own!
+DESC
+  spec.authors      = ["Chris Wanstrath", "Rob Crouch"]
+  spec.license      = "MIT"
+
+  spec.metadata = {
+    "bug_tracker_uri"   => "https://github.com/github/markup/issues",
+    "source_code_uri"   => "https://github.com/github/markup"
+  }
+
+  spec.required_ruby_version = ">= 2.4"
+
+  spec.files         = Dir.glob("lib/**/*", File::FNM_DOTMATCH)
+  spec.executables   = spec.files.grep(%r{^bin/}).map{ |f| File.basename(f) }
+  spec.test_files    = spec.files.grep(%r{^(test|spec|features)/})
+
+  spec.add_development_dependency 'rake', '~> 13.1'
+  spec.add_development_dependency 'activesupport', '~> 7.1', '>= 7.1.3.2'
+  spec.add_development_dependency 'minitest', '~> 5.4', '>= 5.4.3'
+  spec.add_development_dependency 'html-pipeline', '~> 1.0'
+  spec.add_development_dependency "sanitize", "~> 4.6", ">= 4.6.3"
+  spec.add_development_dependency 'nokogiri', '~> 1.8.1'
+  spec.add_development_dependency 'nokogiri-diff', '~> 0.2.0'
+  spec.add_development_dependency "github-linguist", "~> 7.1", ">= 7.1.3"
+
+
+end
\ No newline at end of file
diff --git a/lib/github-markup.rb b/lib/github-markup.rb
index 58f9b1c5..7262d652 100644
--- a/lib/github-markup.rb
+++ b/lib/github-markup.rb
@@ -1,6 +1,6 @@
 module GitHub
   module Markup
-    VERSION = '4.0.2'
+    VERSION = '4.0.3'
     Version = VERSION
   end
 end
diff --git a/lib/github/markup/version.rb b/lib/github/markup/version.rb
new file mode 100644
index 00000000..98a2d3e3
--- /dev/null
+++ b/lib/github/markup/version.rb
@@ -0,0 +1,6 @@
+module GitHub
+  module Markup
+    VERSION = '4.0.3'
+    Version = VERSION
+  end
+end
\ No newline at end of file
diff --git a/lib/github/markups.rb b/lib/github/markups.rb
index 79e53216..df7f4bea 100644
--- a/lib/github/markups.rb
+++ b/lib/github/markups.rb
@@ -48,8 +48,8 @@
   Asciidoctor.convert(content, :safe => :secure, :attributes => attributes)
 end
 
-markup(::GitHub::Markups::MARKUP_RST, :rest2html, /re?st(\.txt)?/, ["reStructuredText"]) do |filename, content, options: {}|
-  PandocRuby.convert(content, :from => 'rst', :to => 'html')
+markup(::GitHub::Markups::MARKUP_RST, :rst, /re?st(\.txt)?/, ["reStructuredText"]) do |filename, content, options: {}|
+  PandocRuby.new(content, from: 'rst').to_html
 end
 
 command(::GitHub::Markups::MARKUP_POD6, :pod62html, /pod6/, ["Pod 6"], "pod6")
diff --git a/script/bootstrap b/script/bootstrap
index f89f3181..6b87f215 100755
--- a/script/bootstrap
+++ b/script/bootstrap
@@ -5,4 +5,4 @@ set -e
 cd $(dirname "$0")/..
 
 bundle install
-pip3 install docutils
+
diff --git a/script/bootstrap.contrib b/script/bootstrap.contrib
index 834b6b61..3c0a38bd 100755
--- a/script/bootstrap.contrib
+++ b/script/bootstrap.contrib
@@ -5,11 +5,8 @@ set -e
 cd $(dirname "$0")/..
 
 bundle install --path vendor/bundle
-virtualenv vendor/python && source vendor/python/bin/activate
-pip install docutils
 
 echo ""
 echo "*** DONE ***"
 echo ""
-echo "activate python environment with 'source vendor/python/bin/activate'"
 echo "run tests with 'bundle exec rake'"
diff --git a/script/cibuild b/script/cibuild
index 33251773..6d6fd2b5 100755
--- a/script/cibuild
+++ b/script/cibuild
@@ -10,7 +10,7 @@ export RUBY_HEAP_SLOTS_INCREMENT=400000
 export RUBY_HEAP_SLOTS_GROWTH_FACTOR=1
 
 export PATH="/usr/share/rbenv/shims:$PATH"
-export RBENV_VERSION="1.9.3"
+export RBENV_VERSION="3.3.0"
 
 # bootstrap gem environment changes
 echo "Bootstrapping gem environment ..."
diff --git a/test/markup_test.rb b/test/markup_test.rb
index 24e78000..bd296ff7 100644
--- a/test/markup_test.rb
+++ b/test/markup_test.rb
@@ -5,6 +5,7 @@
 require 'github/markup'
 require 'minitest/autorun'
 require 'html/pipeline'
+require 'sanitize'
 require 'nokogiri'
 require 'nokogiri/diff'