Revert "Do not use native promise by default."

This reverts commit f47dc87e

lib/rsvp/async.js

@@ -81,14 +81,14 @@ function useSetTimeout() {
   };
 }
 
-if (typeof setImmediate === 'function') {
+if (checkNativePromise()) {
+  async = useNativePromise();
+} else if (typeof setImmediate === 'function') {
   async = useSetImmediate();
 } else if (typeof process !== 'undefined' && {}.toString.call(process) === '[object process]') {
   async = useNextTick();
 } else if (BrowserMutationObserver) {
   async = useMutationObserver();
-} else if (checkNativePromise()) {
-  async = useNativePromise();
 } else {
   async = useSetTimeout();
 }