fix rollup build

Author: Gusted

tsconfig.json

@@ -13,7 +13,8 @@
     "resolveJsonModule": true,
     "declarationDir": "dist/types",
     "outDir": "dist/lib",
-    "typeRoots": ["node_modules/@types"]
+    "typeRoots": ["node_modules/@types"],
+    "downlevelIteration": true,
   },
   "include": ["src/**/*.ts"],
   "exclude": ["node_modules"]