refactor(): use const and let instead of var

modules/@angular/examples/facade/ts/async/observable_patched.ts

@@ -12,8 +12,8 @@ import 'rxjs/add/operator/map';
 import {Observable} from 'rxjs/Observable';
 import {Subscriber} from 'rxjs/Subscriber';
 
-var obs = new Observable<number>((obs: Subscriber<any>) => {
-  var i = 0;
+const obs = new Observable<number>((obs: Subscriber<any>) => {
+  let i = 0;
   setInterval(() => obs.next(++i), 1000);
 });
 obs.map((i: number) => `${i} seconds elapsed`).subscribe(msg => console.log(msg));