docs(get-as-object): minor typo fix (angular#219)

Author: StephenFluin

docs/2-retrieving-data-as-objects.md

@@ -116,7 +116,7 @@ itemObservable.update({ age: newAge });
 ```
 
 **Only objects are allowed for updates, not primitives**. This is because
-using an update with a primitive is the exact same as doing a `.set()` with a primtivie.
+using an update with a primitive is the exact same as doing a `.set()` with a primitive.
 
 ### Deleting data
 Use the `remove()` method to remove data at the object's location.