fix(ScrollView): fix issue with scroll view not scrolling (#872)

Fixes #871

Libraries/Components/ScrollView/ScrollView.windows.js

@@ -558,14 +558,12 @@ const ScrollView = React.createClass({
 
 const styles = StyleSheet.create({
   baseVertical: {
-    flexGrow: 1,
-    flexShrink: 1,
+    flex: 1,
     flexDirection: 'column',
     overflow: 'scroll',
   },
   baseHorizontal: {
-    flexGrow: 1,
-    flexShrink: 1,
+    flex: 1,
     flexDirection: 'row',
     overflow: 'scroll',
   },