replace Dir.exists? w/ File.directory? for Ruby 1.8.7 compat
replace Dir.exists? w/ File.directory? for Ruby 1.8.7 compat

asciidocfx/asciidoctor,yukisan/asciidoctor,neontapir/asciidoctor,benignbala/asciidoctor,cesarmarinhorj/asciidoctor,glamouracademy/asciidoctor,cuit-zhaxin/asciidoctor,mjang/mj-asciidoc,glamouracademy/asciidoctor,anthonny/asciidoctor,pepijnve/asciidoctor,anthonny/asciidoctor,mjang/mj-asciidoc,pepijnve/asciidoctor,neontapir/asciidoctor,gjtorikian/asciidoctor,benignbala/asciidoctor,gjtorikian/asciidoctor,asciidocfx/asciidoctor,cuit-zhaxin/asciidoctor,yukisan/asciidoctor