Improved: fix a PDF generation issue with Buildbot too now

Oops, in previous I also commented out the line, here is the fix

-//        backends = ['html5']
+        backends = ['html5']

BTW, this fixes all AsciidoctorTaskS...

Author: JacquesLeRoux

build.gradle

@@ -564,12 +564,12 @@ tasks.withType(AsciidoctorTask) { task ->
 //        } else {
 //            backends = ['html5', 'pdf']
 //        }
-         //It seems we have no choice when using Builbot we get this issue:
+         //It seems we have no choice when using Builbot we now get this issue:
 //        Caused by: org.jruby.exceptions.LoadError: (LoadError) no such file to load -- asciidoctor-pdf
 //        at org.jruby.RubyKernel.require(org/jruby/RubyKernel.java:1017)
 //        at RUBY.require(uri:classloader:/META-INF/jruby.home/lib/ruby/stdlib/rubygems/core_ext/kernel_require.rb:85)
 //        at RUBY.<main>(<script>:1)
-//        backends = ['html5']
+        backends = ['html5']
     }
     attributes \
         'doctype': 'book',