Remove logged output

[swimmadude66]

This line throws TypeError: Converting circular structure to JSON and there's no way to disable it, even though the config that's used it perfectly valid.

Check that your description matches the automatic change-log format:
http://karma-runner.github.io/latest/dev/git-commit-msg.html
then delete this reminder.

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[johnjbarton]

Configuration errors are common and the config can be changed dynamically by plugins. Logging the final config is a critical step in debugging user issues.

You could:

1. Find a way to log the config without json.stringify.
2. Wrap the stringify line with try/catch and log a debug message that the attempt to log the config failed.

Either way, wrapping the code in a check on the logLevel === debug would be great.

[johnjbarton]

Or we can switch to flatted: https://www.npmjs.com/package/flatted
That would seem to be the best, we can replace json3:
https://github.com/karma-runner/karma/search?q=json3&unscoped_q=json3
and solve your issue as well.