missing '.' in ListView.DataSource example

Summary:
The `ListView.DataSource` example is missing a period. Previously looked like a method i.e.` ListViewDataSource`
Closes https://github.com/facebook/react-native/pull/520
Github Author: Cspeisman <Cspeisman@gmail.com>

Test Plan: Imported from GitHub, without a `Test Plan:` line.

Libraries/CustomComponents/ListView/ListView.js

@@ -61,7 +61,7 @@ var SCROLLVIEW_REF = 'listviewscroll';
  *
  * ```
  * getInitialState: function() {
- *   var ds = new ListViewDataSource({rowHasChanged: (r1, r2) => r1 !== r2});
+ *   var ds = new ListView.DataSource({rowHasChanged: (r1, r2) => r1 !== r2});
  *   return {
  *     dataSource: ds.cloneWithRows(['row 1', 'row 2']),
  *   };