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/resolver.go

@@ -23,10 +23,10 @@ import (
 	"crypto/x509"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"net/http"
 	"net/http/httptrace"
 	"net/http/httputil"
+	"os"
 	"strings"
 
 	"github.com/containerd/console"
@@ -124,7 +124,7 @@ func resolverDefaultTLS(clicontext *cli.Context) (*tls.Config, error) {
 	}
 
 	if tlsRootPath := clicontext.String("tlscacert"); tlsRootPath != "" {
-		tlsRootData, err := ioutil.ReadFile(tlsRootPath)
+		tlsRootData, err := os.ReadFile(tlsRootPath)
 		if err != nil {
 			return nil, errors.Wrapf(err, "failed to read %q", tlsRootPath)
 		}