Don't use 'vertically' when describing a ListView

Summary:
it gives the wrong impression that a ListView has the restriction to only align the items vertically

The problem the PR addresses is that the documentation currently gives the initial impression that a ListView can only stack the items vertically.
Closes https://github.com/facebook/react-native/pull/12564

Differential Revision: D4622096

Pulled By: hramos

fbshipit-source-id: ce634087d143a28904d998a4c7301ca18392714e

docs/UsingAListView.md

@@ -8,7 +8,7 @@ next: network
 previous: using-a-scrollview
 ---
 
-The `ListView` component displays a vertically scrolling list of changing, but similarly structured, data.
+The `ListView` component displays a scrolling list of changing, but similarly structured, data.
 
 `ListView` works well for long lists of data, where the number of items might change over time. Unlike the more generic [`ScrollView`](docs/using-a-scrollview.html), the `ListView` only renders elements that are currently showing on the screen, not all the elements at once.