Replace cross-fetch with whatwg-fetch

We import it conditionally anyway and cross-fetch has an issue where
it's used even in environments where fetch exists natively, see
lquixada/cross-fetch#138

__tests__/withAxiom.test.ts

@@ -1,6 +1,6 @@
 import { withAxiom } from '../src/index';
 import { NextApiRequest, NextApiResponse } from 'next';
-import 'cross-fetch/polyfill';
+import 'whatwg-fetch';
 import { NextFetchEvent, NextRequest, NextResponse } from 'next/server';
 
 test('withAxiom(NextConfig)', async () => {

package.json

@@ -49,6 +49,6 @@
     "typescript": "^4.6.4"
   },
   "dependencies": {
-    "cross-fetch": "^3.1.5"
+    "whatwg-fetch": "^3.6.2"
   }
 }

src/logger.ts

@@ -43,7 +43,7 @@ async function sendLogs() {
 
   try {
     if (typeof fetch === 'undefined') {
-      const fetch = await require('cross-fetch');
+      const fetch = await require('whatwg-fetch');
       await fetch(url, { body, method, keepalive });
     } else if (isBrowser && navigator.sendBeacon) {
       navigator.sendBeacon(url, body);