Convert verb to uppercase

In Google Chrome, `patch` specifically seems to be causing problems. I'd been Googling for about an hour and finally came across this SO post: https://stackoverflow.com/a/67744766/51021

Apparently, some verbs (`PATCH` in my case) ARE case-sensitive when comparing against a pre-flight `OPTIONS` check.

I think in order to be the most compatible with the `axios` module, and to make `PATCH` work during cross-origin requests, these verbs should be made uppercase (See `axios` source: [axios/lib/adapters/xhr.js#L32](https://github.com/axios/axios/blob/5ad6994/lib/adapters/xhr.js#L32))

src/index.js

@@ -196,7 +196,7 @@ export default (function create(/** @type {Options} */ defaults) {
 		const fetchFunc = options.fetch || fetch;
 
 		return fetchFunc(url, {
-			method: _method || options.method,
+			method: (_method || options.method).toUpperCase(),
 			body: data,
 			headers: deepMerge(options.headers, customHeaders, true),
 			credentials: options.withCredentials ? 'include' : 'same-origin'