refactor: move from io/ioutil to io and os package

The io/ioutil package has been deprecated as of Go 1.16, see
https://golang.org/doc/go1.16#ioutil. This commit replaces the existing
io/ioutil functions with their new definitions in io and os packages.

Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>

cmd/ctr/commands/content/content.go

@@ -19,7 +19,6 @@ package content
 import (
 	"fmt"
 	"io"
-	"io/ioutil"
 	"os"
 	"strings"
 	"text/tabwriter"
@@ -519,7 +518,7 @@ func edit(context *cli.Context, rd io.Reader) (io.ReadCloser, error) {
 		return nil, fmt.Errorf("editor is required")
 	}
 
-	tmp, err := ioutil.TempFile(os.Getenv("XDG_RUNTIME_DIR"), "edit-")
+	tmp, err := os.CreateTemp(os.Getenv("XDG_RUNTIME_DIR"), "edit-")
 	if err != nil {
 		return nil, err
 	}