make sure we assign tunnels in the registry

src/ngrok/server/registry.go

@@ -62,6 +62,8 @@ func (r *TunnelRegistry) Register(url string, t *Tunnel) error {
 		return fmt.Errorf("The tunnel %s is already registered.", url)
 	}
 
+	r.tunnels[url] = t
+
 	return nil
 }