react-native: Correct onKeyPress type

See https://facebook.github.io/react-native/docs/0.53/textinput.html#onkeypress
This has been the case since 0.41 at least.

types/react-native/index.d.ts

@@ -972,7 +972,7 @@ export interface TextInputIOSProperties {
      * Pressed key value is passed as an argument to the callback handler.
      * Fires before onChange callbacks.
      */
-    onKeyPress?: (key: string) => void;
+    onKeyPress?: (event: {nativeEvent: {key: string}}) => void;
 
     /**
      * See DocumentSelectionState.js, some state that is responsible for maintaining selection information for a document