hetzner-kube: Adding worker node crashes on OSX (0.3.1-SNAPSHOT)

$ hetzner-kube cluster add-worker --nodes 1 --name iridescent-foerune
2018/06/16 13:26:13 creating server 'iridescent-foerune-worker-02'...
  --- [======================================] 100%
2018/06/16 13:26:36 Created node 'iridescent-foerune-worker-02' with IP *.*.*.*
panic: runtime error: slice bounds out of range

goroutine 1 [running]:
github.com/xetys/hetzner-kube/pkg/clustermanager.PrivateIPPrefix(0x0, 0x0, 0xc42015b668, 0x2)
	/Users/volkerschwaberow/golang/src/github.com/xetys/hetzner-kube/pkg/clustermanager/wireguard.go:64 +0xad
github.com/xetys/hetzner-kube/pkg/hetzner.(*Provider).CreateNodes(0xc4200e8400, 0x14ff9b1, 0x6, 0x0, 0x0, 0x14fdb62, 0x4, 0x0, 0x0, 0x0, ...)
	/Users/volkerschwaberow/golang/src/github.com/xetys/hetzner-kube/pkg/hetzner/hetzner_provider.go:110 +0x675
github.com/xetys/hetzner-kube/pkg/hetzner.(*Provider).CreateWorkerNodes(0xc4200e8400, 0xc4201b1448, 0x3, 0x14fdb62, 0x4, 0xc4201be6c0, 0x3, 0x3, 0x1, 0x1, ...)
	/Users/volkerschwaberow/golang/src/github.com/xetys/hetzner-kube/pkg/hetzner/hetzner_provider.go:146 +0x14b
github.com/xetys/hetzner-kube/cmd.glob..func5(0x17c2e20, 0xc4200b0fc0, 0x0, 0x4)
	/Users/volkerschwaberow/golang/src/github.com/xetys/hetzner-kube/cmd/cluster_add_worker.go:102 +0x5e5
github.com/xetys/hetzner-kube/vendor/github.com/spf13/cobra.(*Command).execute(0x17c2e20, 0xc4200b0f40, 0x4, 0x4, 0x17c2e20, 0xc4200b0f40)
	/Users/volkerschwaberow/golang/src/github.com/xetys/hetzner-kube/vendor/github.com/spf13/cobra/command.go:702 +0x2c6
github.com/xetys/hetzner-kube/vendor/github.com/spf13/cobra.(*Command).ExecuteC(0x17c5020, 0x177c960, 0x0, 0x0)
	/Users/volkerschwaberow/golang/src/github.com/xetys/hetzner-kube/vendor/github.com/spf13/cobra/command.go:783 +0x2e4
github.com/xetys/hetzner-kube/vendor/github.com/spf13/cobra.(*Command).Execute(0x17c5020, 0x14fe4a5, 0x5)
	/Users/volkerschwaberow/golang/src/github.com/xetys/hetzner-kube/vendor/github.com/spf13/cobra/command.go:736 +0x2b
github.com/xetys/hetzner-kube/cmd.Execute()
	/Users/volkerschwaberow/golang/src/github.com/xetys/hetzner-kube/cmd/root.go:51 +0x7e
main.main()
	/Users/volkerschwaberow/golang/src/github.com/xetys/hetzner-kube/main.go:20 +0x20