Add "civo" CLI to "arkade get"

With the Civo CLI re-write in Go, it can now be downloaded with "arkade get":

arkade get civo

• Launch a managed k3s cluster in < 60s with free credits here
• Read more about The World's First Managed k3s Service

Changelog for 0.6.8:

• PR #192 Add CLI for Civo cloud by @alexellis

Commits
a93841d Add CLI for Civo cloud by @alexellis

Generated by Derek