State the Kubernetes version somewhere in the docs

[mcapuccini]

Somewhere in the docs we should state the Kubernetes version that we are using.

[carmat88]

Howdy! In this document here:

• https://github.com/kubenow/docs/blob/master/getting_started/prerequisites.rst

I am wondering to say something along the line of:

KubeNow provisioners are distributed via Docker and based on Kubernetes version 1.9.2-00

What do you think? Cheers.

[mcapuccini]

That'd be great 🙂 (1.9.2, is enough to state)