Set Go version to 1.11.6 for release v0.12.2
Set Go version to 1.11.6 for release v0.12.2

Signed-off-by: Ivan Kozlovic <a15f8b81a160b4eebe5c84e9e3b65c87b9b2f18e@synadia.com>

nats-io/nats-streaming-server,nats-io/nats-streaming-server