Add persistence option to publisher

I've added the persistence options to the publisher publish method. 
In addition I've linted a couple of files with rubocop and removed `Gemfile.lock` (http://yehudakatz.com/2010/12/16/clarifying-the-roles-of-the-gemspec-and-gemfile/). 
In `Rakefile` I've made mapped `default: :test` so that Travis can run CI tests without a `.travis.yml`