Set Java Toolchain to enforce module JVM to 8

[abelsromero]

Otherwise the value of 'org.gradle.jvm.version' is set to the JVM used during build.

[abelsromero]

I see development-4.x branch has a quick fix for the description too, but that is removing the actual description in the POM and simply inserting a dot. I think we should fix it too before any patch release.

[abelsromero]

I think GH is about to crash, I saw the "oops page" and CI is showing weird errors.

I validated the change locally building with JDK 11 and checking the modules

find . -name "asciidoctor-gradle-*.module" -exec cat {} \; | grep 'org.gradle.jvm.version'

Without the fix I saw 11.