Plugin includes multiple versions of the same dependency

[tylerbertrand]

The plugin includes multiple versions of the jruby-complete dependency.

This causes conflicts during dependency resolution, and results in failed builds when applied to a build with failOnVersionConflict enabled.

It looks like this code adds the asciidoctorj dependency, then adds jruby-complete with the version provided by minimumSafeJrubyVersion, which is currently set to 9.1.0.0. I believe this should be updated to 9.3.8.0, which is the version used in asciidoctorj:2.5.7.

Tested against plugin version 4.0.1.