Active opacity for TouchableHighlight should be 0.85 to match iOS native look

Summary:
While working on a feature in realized the buttons I built using `TouchableHighlight` were too dark when pressed.

When used white white views, `TouchableHighlight` produces the color `d4d5d5`. This is different from `dedede` which iOS uses.

Let's use opacity 0.85 instead of 0.8 to make the color match iOS. See a React Native view compared to iOS settings screen (same color for pressed items now): http://imgur.com/a/6CyL3

On Android, people should be using `TouchableNativeFeedback` everywhere.

Reviewed By: sahrens

Differential Revision: D3896168

fbshipit-source-id: a7dd12b4bde079b120faaffc36d25292533a2c6d

Libraries/Components/Touchable/TouchableHighlight.js

@@ -32,7 +32,7 @@ var onlyChild = require('react/lib/onlyChild');
 type Event = Object;
 
 var DEFAULT_PROPS = {
-  activeOpacity: 0.8,
+  activeOpacity: 0.85,
   underlayColor: 'black',
 };