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>

connector/ldap/ldap.go

@@ -7,8 +7,8 @@ import (
 	"crypto/x509"
 	"encoding/json"
 	"fmt"
-	"io/ioutil"
 	"net"
+	"os"
 
 	"github.com/go-ldap/ldap/v3"
 
@@ -257,7 +257,7 @@ func (c *Config) openConnector(logger log.Logger) (*ldapConnector, error) {
 		data := c.RootCAData
 		if len(data) == 0 {
 			var err error
-			if data, err = ioutil.ReadFile(c.RootCA); err != nil {
+			if data, err = os.ReadFile(c.RootCA); err != nil {
 				return nil, fmt.Errorf("ldap: read ca file: %v", err)
 			}
 		}