fixes crash for react native instrumenting fetch (getsentry#2510)

- check for global.document.createElement to be function before  calling

Author: mxs

packages/utils/src/supports.ts

@@ -106,7 +106,7 @@ export function supportsNativeFetch(): boolean {
   // so create a "pure" iframe to see if that has native fetch
   let result = false;
   const doc = global.document;
-  if (doc) {
+  if (doc && typeof doc.createElement === 'function') {
     try {
       const sandbox = doc.createElement('iframe');
       sandbox.hidden = true;