rename task.failed to task.fail

[ryan-linehan]

Hi! Thank you for this awesome plugin! This is a small recommendation of renaming task.failed to task.fail. The tenses of these verbs are not consistent. The past tense of fail is failed. The past tense of succeed is succeeded. If you like the proposal and would like me to make a PR I would be happy to!

[fian46]

Yes we can add new fail but keep failed too so it won't break people project.