Hook WithLevels logic is backwards - Setting AllLevels when WithLevels != nil

[mwuerstlAtFinch]

The slacklogrus.go Levels() func is returning logrus.AllLevels when a WithLevel value was set. The func condition should be:
// Levels sent to slack
func (h *Hook) Levels() []logrus.Level {
if h.WithLevels == nil {
return logrus.AllLevels
}
return h.WithLevels
}

[dwburke]

looks like a new version tag just needs created... this was fixed a year and a week ago