Fix nats-io import path

[asiragusa]

Hi @Jeffail,

Recently nats changed their repositories to https://github.com/nats-io/nats.go and https://github.com/nats-io/stan.go and this breaks go mod. I updated the dependencies, but still can't run go mod tidy because of nats-io/stan.go#280

[asiragusa]

Ok also tests are failing, we must wait for nats-io/stan.go#280

[asiragusa]

@Jeffail it works now, we might still track the original issue to fix the indirect dependency

[Jeffail]

Cool, thanks @asiragusa!