Make gem compatible with ruby 1.8.7 again. Added Travis-ci.org support

I've made the following changes:

* Hash syntax changes so that it will work on ruby 1.8.7
* Added conditional json gem dependencies for ruby 1.8.7
* Added conditional json-jruby and jruby-openssl dependencies for jruby
* Added travis.yml file.

All tests are passing:

https://travis-ci.org/aq1018/stretcher