panic when ctrl+c a node which was started for the first time and it fetched new certs

[jonaz]

panic: close of closed channel

goroutine 52 [running]:
github.com/stampzilla/stampzilla-go/pkg/node.(*Node).fetchCertificate.func1(0xc0000603c0, 0xc0001200c0, 0xc0000131c0)
	/home/jonaz/go/src/github.com/stampzilla/stampzilla-go/pkg/node/node.go:163 +0x15c
created by github.com/stampzilla/stampzilla-go/pkg/node.(*Node).fetchCertificate
	/home/jonaz/go/src/github.com/stampzilla/stampzilla-go/pkg/node/node.go:160 +0x2c4
exit status 2