Fix small typo in the help text

Summary:
Not much to add. My OCD spotted this 😄
Closes https://github.com/facebook/react-native/pull/10275

Differential Revision: D3984542

Pulled By: hramos

fbshipit-source-id: 2de8c8f7f5c2c518e0ec5277087095e0553c72d6

Libraries/CustomComponents/Navigator/Navigator.js

@@ -297,7 +297,7 @@ var Navigator = React.createClass({
      * (route, routeStack) => Navigator.SceneConfigs.FloatFromRight
      * ```
      *
-     * Available scene configutation options are:
+     * Available scene configuration options are:
      *
      *  - Navigator.SceneConfigs.PushFromRight (default)
      *  - Navigator.SceneConfigs.FloatFromRight