Reduce Travis CI matrix
Reduce Travis CI matrix

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