Fix/refactor version command

[mrusme]

The version command is outdated. Goreleaser supports setting the version by using this code:

package main

import "fmt"

var (
    version = "dev"
    commit  = "none"
    date    = "unknown"
)

func main() {
  fmt.Printf("my app %s, commit %s, built at %s", version, commit, date)
}

The dedicated version command is not needed, as Cobra has a Version attribute for the root command that can be used for this.

[mrusme]

On hold due to #43