Keep RSpec configuration between runs

RSpec resets the world and configuration objects after each run
(https://github.com/rspec/rspec-core/blob/master/lib/rspec/core/runner.rb#L83).

So it's better to keep the configuration defined in spec_helper.rb, because this
file is loaded only once (at the first run of guard-jruby-rspec).
Merge pull request #25 from soulim/keep-configuration

Keep RSpec configuration between runs