Bump asciidoctorj from 2.5.5 to 2.5.6

Bumps [asciidoctorj](https://github.com/asciidoctor/asciidoctorj) from 2.5.5 to 2.5.6.
- [Release notes](https://github.com/asciidoctor/asciidoctorj/releases)
- [Changelog](https://github.com/asciidoctor/asciidoctorj/blob/v2.5.6/CHANGELOG.adoc)
- [Commits](asciidoctor/asciidoctorj@v2.5.5...v2.5.6)

---
updated-dependencies:
- dependency-name: org.asciidoctor:asciidoctorj
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

pom.xml

@@ -84,7 +84,7 @@
     <maven-javadoc-plugin.version>3.4.1</maven-javadoc-plugin.version>
     <maven.jar.plugin.version>3.3.0</maven.jar.plugin.version>
     <asciidoctor.maven.plugin.version>2.2.2</asciidoctor.maven.plugin.version>
-    <asciidoctorj.version>2.5.5</asciidoctorj.version>
+    <asciidoctorj.version>2.5.6</asciidoctorj.version>
     <asciidoctorj.pdf.version>2.3.0</asciidoctorj.pdf.version>
     <asciidoctorj.diagram.version>2.2.3</asciidoctorj.diagram.version>
     <buildnumber.plugin.version>1.4</buildnumber.plugin.version>