upgrade Asciidoctor PDF page to 1.5.0.beta.7

Author: mojavelinux

Diff for: docs/asciidoctor-pdf.adoc

@@ -1,6 +1,6 @@
 // NOTE include file is not resolved when reading the header only, hence the extra attributes
 :doctitle: Asciidoctor PDF
-:revnumber: 1.5.0.beta.3
+:revnumber: 1.5.0.beta.7
 :gitref: v{revnumber}
 :page-layout: docs
 :page-keywords: Asciidoctor, PDF, asciidoctor-pdf, AsciiDoc, postscript, converter, themes, Prawn