ReactInstanceManager API Updates

Summary:
Updating code example with updated method names...

`onHostPause` -> `onPause`
`onHostResume` -> `onResume`
`onHostDestroy` -> `onDestroy`
Closes facebook#9217

Differential Revision: D3671267

Pulled By: javache

fbshipit-source-id: 007a2b0909fee4495a98c141bd6ac3a564b50c17

docs/IntegrationWithExistingApps.md

@@ -651,7 +651,7 @@ protected void onPause() {
     super.onPause();
 
     if (mReactInstanceManager != null) {
-        mReactInstanceManager.onHostPause();
+        mReactInstanceManager.onPause();
     }
 }
 
@@ -660,7 +660,7 @@ protected void onResume() {
     super.onResume();
 
     if (mReactInstanceManager != null) {
-        mReactInstanceManager.onHostResume(this, this);
+        mReactInstanceManager.onResume(this, this);
     }
 }
 
@@ -669,7 +669,7 @@ protected void onDestroy() {
     super.onDestroy();
 
     if (mReactInstanceManager != null) {
-        mReactInstanceManager.onHostDestroy();
+        mReactInstanceManager.onDestroy();
     }
 }
 ```