upgraded JRuby, libraries, Maven plugins and RubyGems; fixed upstream test script

- upgraded JRuby to 1.7.16.1
- upgraded Maven plugins
- upgraded libraries (slf4j, jcommander, guava, jsoup)
- upgraded dependent gems (haml, tilt, slim)
- fixed upstream test script
resolves #219 upgrade to Asciidoctor 1.5.2
resolves #202 add oraclejdk8 to Travis CI builds