libct/cg/fscommon: drop go 1.13 compatibility

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

libcontainer/cgroups/fscommon/utils.go

@@ -3,6 +3,7 @@
 package fscommon
 
 import (
+	"errors"
 	"fmt"
 	"math"
 	"path"
@@ -45,10 +46,7 @@ func ParseUint(s string, base, bitSize int) (uint64, error) {
 		// 2. Handle negative values lesser than MinInt64
 		if intErr == nil && intValue < 0 {
 			return 0, nil
-			// Note errors.Is is not working for strconv errors in Go 1.13,
-			// see https://github.com/golang/go/issues/36325.
-			// TODO: remove nolint and switch to errors.Is once we stop supporting Go 1.13.
-		} else if intErr != nil && intErr.(*strconv.NumError).Err == strconv.ErrRange && intValue < 0 { //nolint:errorlint
+		} else if errors.Is(intErr, strconv.ErrRange) && intValue < 0 {
 			return 0, nil
 		}