Not removing self as an observer

[Gasper]

Basically what it says in the title. Would gladly open a pull request when I have 15 min to breathe :) Otherwise this is the snippet:

deinit {
    AVAudioSession.sharedInstance().removeObserver(self, forKeyPath: "outputVolume", context: nil)
}

[Andrea Mazzini]

Hi @gapl
My bad! I'll push a fixed version right away. Thanks for the heads up 👍