Gemfile in asciidoctor-epub3-1.5.0.alpha.7 vs Gemfile in asciidoctor-epub3-1.5.0.alpha.8

@@ -2,9 +2,14 @@
 
 # Look in asciidoctor-epub3.gemspec for runtime and development dependencies.
 gemspec
 
 group :optional do
-  gem 'pygments.rb', '1.1.1'
-  gem 'kindlegen', '3.0.3'
   gem 'epubcheck', '3.0.1'
+  if (ruby_version = Gem::Version.new RUBY_VERSION) < (Gem::Version.new '2.0.0')
+    gem 'kindlegen', '2.9.4'
+    gem 'pygments.rb', '0.6.3'
+  else
+    gem 'kindlegen', '3.0.3'
+    gem 'pygments.rb', '1.1.2'
+  end
 end