Set stdout correctly (#232)

The `cmd.Do` function takes a writer to use as standard out, but doesn't
use it. Instead, there's a duplicate call to `cobra.Command.SetErr`.
This patch replaces one of the duplicates with `SetOut`.

internal/cmd/cmd.go

@@ -29,7 +29,7 @@ func Do(args []string, stdin io.Reader, stdout io.Writer, stderr io.Writer) int
 
 	rootCmd.SetArgs(args)
 	rootCmd.SetIn(stdin)
-	rootCmd.SetErr(stderr)
+	rootCmd.SetOut(stdout)
 	rootCmd.SetErr(stderr)
 
 	err := rootCmd.Execute()