Update gem dependencies version

Author: networm

Gemfile

@@ -1,13 +1,13 @@
 source 'https://rubygems.org'
 
 gem 'rake'
-gem 'asciidoctor', '1.5.6.1'
+gem 'asciidoctor', '1.5.6.2'
 
 gem 'json'
 gem 'awesome_print'
 
-gem 'asciidoctor-epub3', :git => 'https://github.com/asciidoctor/asciidoctor-epub3'
-gem 'asciidoctor-pdf', '1.5.0.alpha.16'
+gem 'asciidoctor-epub3', '~> 1.5.0.alpha.9'
+gem 'asciidoctor-pdf', '~> 1.5.0.beta.8'
 gem 'asciidoctor-pdf-cjk', '~> 0.1.3'
 gem 'asciidoctor-pdf-cjk-kai_gen_gothic', '~> 0.1.1'