Update activity lifecycle callback example

Summary:
Updates the documentation for the the android life cycle methods, recent changes has deprecated

 `onHostPause()` for `onHostPause(Activity activity)`
 `onHostDestroy()` for `onHostDestroy(Activity activity)`

[deprecation commit](https://github.com/facebook/react-native/commit/0b5c61250b290e78b2c37c7c22b8146056cd30d8)
Closes https://github.com/facebook/react-native/pull/10460

Differential Revision: D4044420

Pulled By: JoelMarcey

fbshipit-source-id: 54c5fc8fcd332235b6c0237a180e0c5bb2310a20

docs/IntegrationWithExistingApps.md

@@ -667,7 +667,7 @@ protected void onPause() {
     super.onPause();
 
     if (mReactInstanceManager != null) {
-        mReactInstanceManager.onPause();
+        mReactInstanceManager.onPause(this);
     }
 }
 
@@ -685,7 +685,7 @@ protected void onDestroy() {
     super.onDestroy();
 
     if (mReactInstanceManager != null) {
-        mReactInstanceManager.onDestroy();
+        mReactInstanceManager.onDestroy(this);
     }
 }
 ```