cleanup deprecated package io/ioutil (#4920)

Signed-off-by: zounengren <zouyee1989@gmail.com>

plugin/pkg/tls/tls.go

@@ -4,9 +4,9 @@ import (
 	"crypto/tls"
 	"crypto/x509"
 	"fmt"
-	"io/ioutil"
 	"net"
 	"net/http"
+	"os"
 	"time"
 )
 
@@ -95,7 +95,7 @@ func loadRoots(caPath string) (*x509.CertPool, error) {
 	}
 
 	roots := x509.NewCertPool()
-	pem, err := ioutil.ReadFile(caPath)
+	pem, err := os.ReadFile(caPath)
 	if err != nil {
 		return nil, fmt.Errorf("error reading %s: %s", caPath, err)
 	}