Switch example to github.com/spf13/cobra-cli

[liggitt]

https://github.com/Kevin-fqh/learning-k8s-source-code/blob/master/Go-package%E4%BD%BF%E7%94%A8/%E5%9F%BA%E4%BA%8Ecobra%E6%9E%84%E5%BB%BA%E5%91%BD%E4%BB%A4%E8%A1%8C.md references github.com/spf13/cobra/cobra

That is moving to github.com/spf13/cobra-cli. See spf13/cobra#1597 for details.

Use would look like this:

go get github.com/spf13/cobra-cli

./bin/cobra-cli init cobra_example