fix: Check for global.fetch before binding it (#674)

Author: bbosiljcic

browser.js

@@ -16,7 +16,9 @@ var global = getGlobal();
 module.exports = exports = global.fetch;
 
 // Needed for TypeScript and Webpack.
-exports.default = global.fetch.bind(global);
+if (global.fetch) {
+	exports.default = global.fetch.bind(global);
+}
 
 exports.Headers = global.Headers;
 exports.Request = global.Request;