Add `addRiskyTest` to listener implementation

The `addRiskyTest` method from `PHPUnit_Framework_TestListener` was missing from the example implementation. My translations may need to be checked over though.

 - [ ] Check message "Test '%s' is deemed risky" (`en`, `fr`, `zh_cn`)
 - [ ] Check message "テスト '%s' は危険です" (`jp`)
 - [ ] Check message "O Teste '%s' é arriscado" (`pt_br`)