Implement isomorphic fetch

package.json

@@ -25,8 +25,8 @@
     "@octokit/endpoint": "^7.0.0",
     "@octokit/request-error": "^3.0.0",
     "@octokit/types": "^6.16.1",
+    "cross-fetch": "^3.1.5",
     "is-plain-object": "^5.0.0",
-    "node-fetch": "^2.6.7",
     "universal-user-agent": "^6.0.0"
   },
   "devDependencies": {

src/fetch-wrapper.ts

@@ -1,5 +1,6 @@
 import { isPlainObject } from "is-plain-object";
-import nodeFetch, { HeadersInit, Response } from "node-fetch";
+import isomorphicFetch, { Response } from "cross-fetch";
+import { HeadersInit } from "node-fetch";
 import { RequestError } from "@octokit/request-error";
 import { EndpointInterface } from "@octokit/types";
 
@@ -26,8 +27,8 @@ export default function fetchWrapper(
   let status: number;
   let url: string;
 
-  const fetch: typeof nodeFetch =
-    (requestOptions.request && requestOptions.request.fetch) || nodeFetch;
+  const fetch: typeof isomorphicFetch =
+    (requestOptions.request && requestOptions.request.fetch) || isomorphicFetch;
 
   return fetch(
     requestOptions.url,

src/get-buffer-response.ts

@@ -1,4 +1,4 @@
-import { Response } from "node-fetch";
+import { Response } from "cross-fetch";
 export default function getBufferResponse(response: Response) {
   return response.arrayBuffer();
 }

test/request.test.ts

@@ -3,7 +3,8 @@ import stream from "stream";
 
 import { getUserAgent } from "universal-user-agent";
 import fetchMock from "fetch-mock";
-import { Headers, RequestInit } from "node-fetch";
+import { Headers } from "cross-fetch";
+import { RequestInit } from "node-fetch";
 import { createAppAuth } from "@octokit/auth-app";
 import lolex from "lolex";
 import {