lock Nokogiri version to ~> 1.5.10
lock Nokogiri version to ~> 1.5.10

- cannot install Nokogiri 1.6.0 on Ruby 1.8.7
- Nokogiri 1.6.0 currently incompatible w/ JRuby

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