fix a require error in Rax babel config scenes

Author: Seiry Yu

packages/isomorphic-unfetch/index.js

@@ -1,5 +1,5 @@
 module.exports = global.fetch = global.fetch || (
 	typeof process=='undefined' ? (require('unfetch').default || require('unfetch')) : (function(url, opts) {
-		return require('node-fetch')(url.replace(/^\/\//g,'https://'), opts);
+		return (require('node-fetch').default || require('node-fetch'))(url.replace(/^\/\//g,'https://'), opts);
 	})
 );