add missing props

Summary: Closes https://github.com/facebook/react-native/pull/13717

Differential Revision: D4978002

Pulled By: javache

fbshipit-source-id: 685bb3bf207c858302c74de4cc711b526a80d894

docs/NativeComponentsIOS.md

@@ -305,7 +305,7 @@ You can see we're adding an event handler property to the view by subclassing `M
 // MapView.js
 
 class MapView extends React.Component {
-  constructor() {
+  constructor(props) {
     super(props)
     this._onChange = this._onChange.bind(this);
   }