use specific Ruby versions in Travis builds
use specific Ruby versions in Travis builds

cuit-zhaxin/asciidoctor,neontapir/asciidoctor,yukisan/asciidoctor,benignbala/asciidoctor,glamouracademy/asciidoctor,neontapir/asciidoctor,pepijnve/asciidoctor,asciidocfx/asciidoctor,yukisan/asciidoctor,cuit-zhaxin/asciidoctor,asciidocfx/asciidoctor,anthonny/asciidoctor,glamouracademy/asciidoctor,anthonny/asciidoctor,pepijnve/asciidoctor,benignbala/asciidoctor