Test change in PluralRules default options semantics (#1350)

The change is done in the following patch, where default options
have a null prototype. This matches what other Intl objects have.
https://github.com/tc39/proposal-intl-plural-rules/commit/1abe8af440fb47d888ace701e8a46559bdbe7b06

test/intl402/PluralRules/default-options-object-prototype.js

+// Copyright (C) 2017 Igalia, S. L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-initializepluralrules
+description: >
+  Monkey-patching Object.prototype does not change the default
+  options for PluralRules as a null prototype is used.
+info: >
+  InitializePluralRules ( collator, locales, options )
+
+    1. If _options_ is *undefined*, then
+      1. Let _options_ be ObjectCreate(*null*).
+---*/
+
+Object.prototype.type = "ordinal";
+let pluralRules = new Intl.PluralRules("en");
+assert.sameValue(pluralRules.resolvedOptions().type, "cardinal");