Bump asciidoctorj-pdf from 2.3.7 to 2.3.9 (#391)

Co-authored-by: Boni Garcia <[email protected]>

Author: dependabot[bot]

pom.xml

@@ -29,7 +29,7 @@
         <maven-gpg-plugin.version>3.1.0</maven-gpg-plugin.version>
         <exec-maven-plugin.version>3.0.0</exec-maven-plugin.version>
         <maven-asciidoctor-plugin.version>2.2.4</maven-asciidoctor-plugin.version>
-        <asciidoctorj-pdf.version>2.3.7</asciidoctorj-pdf.version>
+        <asciidoctorj-pdf.version>2.3.9</asciidoctorj-pdf.version>
         <maven-site.version>3.12.1</maven-site.version>
         <maven-project-info-reports.version>3.4.5</maven-project-info-reports.version>
         <maven-javadoc-plugin.version>3.5.0</maven-javadoc-plugin.version>