Update reference to github.com/spf13/cobra/cobra

[liggitt]

https://github.com/codeedu/imersao-fullstack-fullcycle/blob/main/codepix/Dockerfile references go get github.com/spf13/cobra/cobra

The CLI command package has moved to github.com/spf13/cobra-cli. See spf13/cobra#1597 for details.

To install the CLI, switch to go get github.com/spf13/cobra-cli

To install the library, shorten to go get github.com/spf13/cobra