Merge pull request react-navigation#181 from ashinzekene/patch-1

Update stack-navigator.md

Author: brentvatne

docs/stack-navigator.md

@@ -107,7 +107,7 @@ React Element to display on the right side of the header.
 
 #### `headerLeft`
 
-React Element or Component to display on the left side of the header. When a component is used, it receives a number of props when rendered (`onPress`, `title`, `titleStyle` and more - check `Header.js` for the complete list).
+React Element or Component to display on the left side of the header. When a component is used, it receives a number of props when rendered (`onPress`, `title`, `titleStyle` and more - check [Header.js](https://github.com/react-navigation/react-navigation/blob/master/src/views/Header/Header.js) for the complete list).
 
 #### `headerStyle`