Update jsoniter.go (#1500)

add newencoder to fix compile error for -tags=jsoniter

json/jsoniter.go

@@ -13,4 +13,5 @@ var (
 	Marshal       = json.Marshal
 	MarshalIndent = json.MarshalIndent
 	NewDecoder    = json.NewDecoder
+	NewEncoder    = json.NewEncoder
 )