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

- add oraclejdk8 to Travis CI builds
- reduce JVM memory settings
Merge pull request #214 from mojavelinux/jruby-upgrade

upgrade JRuby version to 1.7.16.1
resolves #192 Use classpath-relative files in test suite

- Create helper for resolving test files from classpath
- Added JUnit rule to resolve files relative to classpath
use ClasspathResources to resolve paths for cli tests
add slf4j-simple to test runtime
use modern fork settings for surefire