fix: global fetch

Author: zzswang

packages/fetch/src/index.js

@@ -2,7 +2,7 @@ import realFetch from "node-fetch";
 import wrapper from "./wrapper";
 
 if (!global.fetch) {
-  global.fetch = module.exports;
+  global.fetch = realFetch;
   global.Response = realFetch.Response;
   global.Headers = realFetch.Headers;
   global.Request = realFetch.Request;

packages/fetch/src/wrapper.js

@@ -2,8 +2,6 @@ import qs from "qs";
 import { pickBy, identity } from "lodash";
 import createError from "http-errors";
 
-const realFetch = fetch || window.fetch || global.fetch;
-
 /**
  * A wrapper of fetch
  *
@@ -23,7 +21,7 @@ export default async function(url, opt = {}) {
     ...headers,
   };
 
-  const res = await realFetch(
+  const res = await fetch(
     endpoint,
     pickBy(
       {