RuntimeOptions should also clobber the formatters

When overriding the arguments from the command line/```@CucumberOptions``` annotation with ```cucumber.options``` system property, all options that can hold multiple value are clobbered if provided in system property, except for the formatters option. That is the glue paths, the feature paths and the tag/line/name filters are clobbered if provided in the system property, but not the formatters.

That the formatters should also be formatters is indicated in the [Specify a different formatter](https://github.com/cucumber/cucumber-jvm/tree/master/examples/java-helloworld#specify-a-different-formatter) section of the ReadMe file of the example java-helloworld. The current behaviour is more accurately describes as "Specify an additional formatter".