Update runc to v1.0.0-rc91

https://github.com/opencontainers/runc/releases/tag/v1.0.0-rc91

Signed-off-by: Davanum Srinivas <davanum@gmail.com>

vendor/github.com/json-iterator/go/reflect_extension.go

@@ -341,7 +341,7 @@ func describeStruct(ctx *ctx, typ reflect2.Type) *StructDescriptor {
 		if ctx.onlyTaggedField && !hastag && !field.Anonymous() {
 			continue
 		}
-		if tag == "-" {
+		if tag == "-" || field.Name() == "_" {
 			continue
 		}
 		tagParts := strings.Split(tag, ",")