add license to gemspec
minor readme updates -> capital JRuby-Rack + use at least JRuby 1.6.8
test against resque 1.25 (latest) 1.23 and master & delyed_job 2.1 / 3.0 / 4.0
need to stub `redis.pipelined` on 1.25 (as well besides 2.0.x)