Update to go1.16

pkg/tls/certificate.go

@@ -4,7 +4,6 @@ import (
 	"crypto/tls"
 	"crypto/x509"
 	"fmt"
-	"io/ioutil"
 	"os"
 	"sort"
 	"strings"
@@ -90,7 +89,7 @@ func (f FileOrContent) Read() ([]byte, error) {
 	var content []byte
 	if f.IsPath() {
 		var err error
-		content, err = ioutil.ReadFile(f.String())
+		content, err = os.ReadFile(f.String())
 		if err != nil {
 			return nil, err
 		}