Use rspec and fix percolations for elasticsearch 1 dot 0

Fix percolation for ElasticSearch 1.0+ (re: http://www.elasticsearch.org/blog/percolator-redesign-blog-post/), switch test framework to rspec.
@f1sherman Just that 2.1.1 is preinstalled (vs. available-as-a-binary-but-not-preinstalled), so it's a bit faster: http://docs.travis-ci.com/user/languages/ruby/#Supported-Ruby-Versions