fix(babel): fix an issue where babel could not compile Scheduler.async (#1807)

This moves the `async` property to be the last one defined, because babel will then not choke on the `,` after the property.

fixes #1806

Author: benlesh

src/Rx.ts

@@ -187,9 +187,9 @@ import observable from 'symbol-observable';
  */
 let Scheduler = {
   asap,
-  async,
   queue,
-  animationFrame
+  animationFrame,
+  async
 };
 
 /**