Fix example

Author: 38elements

doc/api/core/operators/elementatordefault.md

@@ -14,7 +14,7 @@ Returns the element at a specified index in a sequence.
 ```js
 /* Finds an index */
 var source = Rx.Observable.from([1,2,3,4])
-    .elementAt(1);
+    .elementAtOrDefault(1);
 
 var subscription = source.subscribe(
     function (x) {
@@ -32,7 +32,7 @@ var subscription = source.subscribe(
 
 /* Not found */
 var source = Rx.Observable.from([1,2,3,4])
-    .elementAt(4, 0);
+    .elementAtOrDefault(4, 0);
 
 var subscription = source.subscribe(
     function (x) {