Replace jruby-parser

[camertron]

Unfortunately jruby-parser hasn't been updated for quite some time, its last release being in 2014. Because of this, Scuttle's model introspection feature breaks when run on modern Ruby code (i.e. > 2.0). I tweeted at the JRuby maintainers, but sadly nothing came of it. I think we'll probably want to upgrade to using the parser in JRuby proper instead of the jruby-parser gem.