Bump org.asciidoctor:asciidoctorj from 2.5.11 to 2.5.13

Bumps [org.asciidoctor:asciidoctorj](https://github.com/asciidoctor/asciidoctorj) from 2.5.11 to 2.5.13.
- [Release notes](https://github.com/asciidoctor/asciidoctorj/releases)
- [Changelog](https://github.com/asciidoctor/asciidoctorj/blob/v2.5.13/CHANGELOG.adoc)
- [Commits](https://github.com/asciidoctor/asciidoctorj/compare/v2.5.11...v2.5.13)

---
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>

spec/pom.xml

diff --git a/spec/pom.xml b/spec/pom.xml
index c9941a6..bad63df 100644
--- a/spec/pom.xml
+++ b/spec/pom.xml
@@ -82,7 +82,7 @@
     <properties>
         <site.output.dir>${project.build.directory}/staging</site.output.dir>
         <maven.site.skip>true</maven.site.skip>
-        <asciidoctorj.version>2.5.11</asciidoctorj.version>
+        <asciidoctorj.version>2.5.13</asciidoctorj.version>
         <asciidoctorj.pdf.version>2.3.13</asciidoctorj.pdf.version>
         <jruby.version>9.3.2.0</jruby.version>
         <!-- status: DRAFT, BETA, etc., or blank for final -->