added support for non2xx3xx error line

I'll happily remove the whitespace changes if those matter to you. Also the factoring out of `handleErrors` may not agree with you. If you'd like to take another approach feel free to convey it and I'll change this pull request. Otherwise this is just a fix for another line type that can occur in `wrk`. Would love to see a release for this whenever you get around to merging it. Thanks!