Fix #110 add CUPRITE_DEBUG back

Author: route

lib/capybara/cuprite/driver.rb

@@ -26,6 +26,8 @@ def initialize(app, options = {})
       @screen_size ||= DEFAULT_MAXIMIZE_SCREEN_SIZE
 
       @options[:save_path] = Capybara.save_path.to_s if Capybara.save_path
+
+      ENV["FERRUM_DEBUG"] = "true" if ENV["CUPRITE_DEBUG"]
     end
 
     def needs_server?