Upgrade to the latest version of asciidoctorj-diagram

[robertpanzer]

Thank you for opening a pull request and contributing to AsciidoctorJ!

Please take a bit of time giving some details about your pull request:

Kind of change

• [ ] Bug fix
• [x] New non-breaking feature
• [ ] New breaking feature
• [ ] Documentation update
• [ ] Build improvement

Description

What is the goal of this pull request?

Upgrade asciidoctorj-diagram to the latest and greatest.

How does it achieve that?

Are there any alternative ways to implement this?

Are there any implications of this pull request? Anything a user must know?

Issue

If this PR fixes an open issue, please add a line of the form:

Fixes #Issue

Release notes

Please add a corresponding entry to the file CHANGELOG.adoc