fix(esm): Corrects .default bug when importing the package

Author: youneshenni

package.json

@@ -20,6 +20,7 @@
     "url": "https://github.com/woocommerce/woocommerce-rest-api-js-lib/issues"
   },
   "main": "index",
+  "module": "index.mjs",
   "types": "index.d.ts",
   "files": [
     "index.js",