Fixed cucumber#520: fix incorrect html formatter behaviour when backg…

…round step fails

When encountering a failure in a background step, the html formatter
incorrectly marked the previous scenario red. With this fix, the html
formatter now correctly marks the current background red and does not
touch the output of the previous scenario anymore.

lib/cucumber/formatter/html.rb

@@ -417,15 +417,17 @@ def set_scenario_color_failed
         @builder.script do
           @builder.text!("makeRed('cucumber-header');") unless @header_red
           @header_red = true
-          @builder.text!("makeRed('scenario_#{@scenario_number}');") unless @scenario_red
+          scenario_or_background = @in_background ? "background" : "scenario"
+          @builder.text!("makeRed('#{scenario_or_background}_#{@scenario_number}');") unless @scenario_red
           @scenario_red = true
         end
       end
 
       def set_scenario_color_pending
         @builder.script do
           @builder.text!("makeYellow('cucumber-header');") unless @header_red
-          @builder.text!("makeYellow('scenario_#{@scenario_number}');") unless @scenario_red
+          scenario_or_background = @in_background ? "background" : "scenario"
+          @builder.text!("makeYellow('#{scenario_or_background}_#{@scenario_number}');") unless @scenario_red
         end
       end