Use kill event instead overriding the .kill()

[persidskiy]

Hi, After Karma#11.11 (e6f36ca) the .kill() metdod of launcher must return promise, otherwise the attempt to kill browser crashes on this step with

TypeError: Cannot call method 'then' of undefined

We can use asyc kill-event to kill the browser instead of overriding .kill() method.

[iknite]

We are dealing with the same just now, and the fix works like a charm, kudos @Coltspb you same me a headache!

[arikon]

:+1:

[aparkinson]

Thanks you for the Pull Request