diff --git a/Gemfile b/Gemfile
index d3ce661..fda906b 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,20 +1,17 @@
 source 'https://rubygems.org'
 
-gem 'rake'
-gem 'asciidoctor', '1.5.6.1'
+gem 'rake', '13.0.6'
+gem 'asciidoctor', '2.0.16'
 
-gem 'json'
-gem 'awesome_print'
+gem 'json', '2.6.1'
+gem 'awesome_print', '1.9.2'
 
-gem 'asciidoctor-epub3', :git => 'https://github.com/asciidoctor/asciidoctor-epub3'
-gem 'asciidoctor-pdf', '1.5.0.alpha.16'
-gem 'asciidoctor-pdf-cjk', '~> 0.1.3'
-gem 'asciidoctor-pdf-cjk-kai_gen_gothic', '~> 0.1.1'
+gem 'asciidoctor-epub3', '1.5.1'
+gem 'asciidoctor-pdf', '1.6.1'
 
-gem 'coderay'
-gem 'pygments.rb'
-gem 'thread_safe'
-gem 'epubcheck'
-gem 'kindlegen'
-
-gem 'octokit'
+gem 'coderay', '1.1.3'
+gem 'pygments.rb', '2.2.0'
+gem 'thread_safe', '0.3.6'
+gem 'epubcheck-ruby', '4.2.6.0'
+gem 'html-proofer', '3.19.3'
+gem 'kindlegen', '3.1.1'