use bundler when testing -r flag; add test for -r asciidoctor/pdf
use bundler when testing -r flag; add test for -r asciidoctor/pdf

Hextremist/asciidoctor-pdf,asciidoctor/asciidoctor-pdf,Hextremist/asciidoctor-pdf,asciidoctor/asciidoctor-pdf,dsisnero/asciidoctor-pdf,mojavelinux/asciidoctor-pdf,dsisnero/asciidoctor-pdf,mojavelinux/asciidoctor-pdf