remove deprecated ioutil module

main.go

@@ -5,7 +5,6 @@ import (
 	"fmt"
 	"image"
 	"io"
-	"io/ioutil"
 	"os"
 	"os/exec"
 	"path/filepath"
@@ -98,7 +97,7 @@ func run() error {
 	if err := tpl.Execute(fplist, info); err != nil {
 		return errors.Wrap(err, "execute Info.plist template")
 	}
-	if err := ioutil.WriteFile(filepath.Join(contentsPath, "README"), []byte(readme), 0666); err != nil {
+	if err := os.WriteFile(filepath.Join(contentsPath, "README"), []byte(readme), 0666); err != nil {
 		return errors.Wrap(err, "ioutil.WriteFile")
 	}
 	return nil