Default scrollview to flexShrink to allow views below it

Summary: Changing from flex -> flexGrow on Scrollview caused some layouts to break due to having views below the scrollview. Adding flexShrink allows for the behavior again.

Reviewed By: blairvanderhoof

Differential Revision: D3936963

fbshipit-source-id: 0f43e6f5148918d3d431b98d26d185bbcc1548d0

Libraries/Components/ScrollView/ScrollView.js

@@ -546,11 +546,13 @@ const ScrollView = React.createClass({
 const styles = StyleSheet.create({
   baseVertical: {
     flexGrow: 1,
+    flexShrink: 1,
     flexDirection: 'column',
     overflow: 'scroll',
   },
   baseHorizontal: {
     flexGrow: 1,
+    flexShrink: 1,
     flexDirection: 'row',
     overflow: 'scroll',
   },