Cucumber tests are not used for mutation testing

[vincent-fuchs]

As mentionned in this plugin by @alexvictoor (https://github.com/alexvictoor/pitest-cucumber-plugin), Cucumber tests are not taken into account by PIT when running a mutation analysis. Similarly, the IntelliJ plugin currently doesn't run the Cucumber tests, and therefore a lot of mutations survive, while the Cucumber tests are actually supposed to kill them.

It would be great if similarly as pitest-cucumber-plugin, the plugin was taking Cucumber tests into account : the final result would be much more accurate.