Add javadoc hotfix plugin as we still compile with JDK6
Add javadoc hotfix plugin as we still compile with JDK6

ysb33r/asciidoctor-gradle-plugin,ysb33r/asciidoctor-gradle-plugin,asciidoctor/asciidoctor-gradle-plugin,ysb33r/asciidoctor-gradle-plugin,asciidoctor/asciidoctor-gradle-plugin,asciidoctor/asciidoctor-gradle-plugin,asciidoctor/asciidoctor-gradle-plugin,ysb33r/asciidoctor-gradle-plugin,mojavelinux/asciidoctor-gradle-plugin,asciidoctor/asciidoctor-gradle-plugin,ysb33r/asciidoctor-gradle-plugin