Merge pull request #1646 from progit/dependabot/bundler/asciidoctor-epub3-1.5.1

Update asciidoctor-epub3 requirement from 1.5.0.alpha.19 to 1.5.1

Author: ben

Gemfile

@@ -6,7 +6,7 @@ gem 'asciidoctor', '2.0.15'
 gem 'json', '2.5.1'
 gem 'awesome_print', '1.9.2'
 
-gem 'asciidoctor-epub3', '1.5.0.alpha.19'
+gem 'asciidoctor-epub3', '1.5.1'
 gem 'asciidoctor-pdf', '1.6.0'
 
 gem 'coderay', '1.1.3'