[Bug] --singleton option prevent venus from running tests

[Baptouuuu]

A few days back, venus stopped running my tests on travis-ci. The only modification since my last run was the release of venus 2.3.2, but even by downgrading back to 2.3.1 I was still having my problem.

I runned my tests with the command venus run -t tests/ -c -n --singleton, the problem was that venus did not output any content but still exited via a code 0.

So I looked back at the venus documentation, but did not find anything about the singleton option; and tried to remove it from the command. It solved my problem!
I looked a bit about what changed recently in the code around this option, but I don't see any important changes that may break it. I'm not that much into server side javascript, so if someone skilled want to look at this, go ahead.

I don't propose any solution on this issue, but it may helps others having the same problem.