replace github.com/cloudfoundry-community/go-cfclient with github.com/cloudfoundry/go-cfclient

[nbinderSTACKIT]

As the cloudfoundry-community client doesnt exist any more, the client should be replaced by the official client.

[gogolok]

Most recent go-cfclient v3 has a different API. So it's a little more work than simple update in go.dep.