Merge pull request react-navigation#183 from react-navigation/tab-docs

Updated tab navigator docs

Author: brentvatne

docs/material-bottom-tab-navigator.md

@@ -78,10 +78,9 @@ ID to locate this tab button in tests.
 
 #### `tabBarOnPress`
 
-Callback to handle tap events; the argument is an object containing:
+Callback to handle press events; the argument is an object containing:
 
-* the `previousScene: { route, index }` which is the scene we are leaving
-* the `scene: { route, index }` that was tapped
-* the `jumpToIndex` method that can perform the navigation for you
+* `navigation`: navigation prop for the screen
+* `defaultHandler`: the default handler for tab press
 
 Useful for adding a custom logic before the transition to the next scene (the tapped one) starts.