Created rack_test_json/dsl_spec.rb and httpclient_json/dsl_spec.rb
Fixed driver_examples.rb not to use 'capybara/spec/driver' because the file does not exist on capybara 2.0.x. Now test passes in both capybara 1.x and capybara 2.x
Main codes
Fixed a bug that DSL body does not work on capybara 2
Fixed a bug that DSL status_code does not exist on capybara 1
Created test codes for DSL to fix #9.
Test Codes.
Main codes
body
does not work on capybara 2status_code
does not exist on capybara 1