Bump asciidoctorj-pdf from 1.6.2 to 2.1.2

Bumps [asciidoctorj-pdf](https://github.com/asciidoctor/asciidoctorj-pdf) from 1.6.2 to 2.1.2.
- [Release notes](https://github.com/asciidoctor/asciidoctorj-pdf/releases)
- [Commits](asciidoctor/asciidoctorj-pdf@v1.6.2...v2.1.2)

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

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

docs/reference/pom.xml

@@ -29,7 +29,7 @@
 
     <properties>
         <asciidoctor.version>2.2.2</asciidoctor.version>
-        <asciidoctorj-pdf.version>1.6.2</asciidoctorj-pdf.version>
+        <asciidoctorj-pdf.version>2.1.2</asciidoctorj-pdf.version>
         <pdf.name>weld-reference.pdf</pdf.name>
         <html.name>index.html</html.name>
         <weld.version>${project.version}</weld.version>