Fix native Object.is() detection, fixes #54.

Author: asudoh

features.js

@@ -3,7 +3,7 @@ define(["requirejs-dplugins/has"], function (has) {
 	has.add("console-api", typeof console !== "undefined");
 	has.add("host-browser", typeof window !== "undefined");
 	has.add("object-observe-api", typeof Object.observe === "function" && typeof Array.observe === "function");
-	has.add("object-is-api", Object.is);
+	has.add("object-is-api", !!Object.is);
 	has.add("setimmediate-api", typeof setImmediate === "function");
 	has.add("mutation-observer-api",
 		typeof MutationObserver !== "undefined"