fix: Have unique error messages for xhr timeouts and errors (#1380)

fetch.js

@@ -563,7 +563,7 @@ export function fetch(input, init) {
 
     xhr.ontimeout = function() {
       setTimeout(function() {
-        reject(new TypeError('Network request failed'))
+        reject(new TypeError('Network request timed out'))
       }, 0)
     }
 
@@ -638,4 +638,4 @@ if (!g.fetch) {
   g.Headers = Headers
   g.Request = Request
   g.Response = Response
-}
+}