Fix: Response.error().ok === false (#1412)

Author: jrmann100

fetch.js

@@ -493,6 +493,7 @@ Response.prototype.clone = function() {
 
 Response.error = function() {
   var response = new Response(null, {status: 200, statusText: ''})
+  response.ok = false
   response.status = 0
   response.type = 'error'
   return response

test/test.js

@@ -696,6 +696,7 @@ exercise.forEach(function(exerciseMode) {
       test('error creates error Response', function() {
         var r = Response.error()
         assert(r instanceof Response)
+        assert.equal(r.ok, false)
         assert.equal(r.status, 0)
         assert.equal(r.statusText, '')
         assert.equal(r.type, 'error')