[patch] make handler for promptForPushNotificationsWithUserResponse required in index.d.ts

The original types suggest that the handler is optional. However, running `OneSignal.promptForPushNotificationsWithUserRespons()`(without providing a handler) results in an "Invariant Violation: A valid callback must be supplied" error.

Seeing as all the other methods have their handlers as required, I figured the bug was with the types and not the actual implementation.

Author: IkeyBenz

src/index.d.ts

@@ -166,7 +166,7 @@ declare module 'react-native-onesignal' {
          * @param  {(response:boolean)=>void} handler
          * @returns void
          */
-        promptForPushNotificationsWithUserResponse(handler?: (response: boolean) => void): void;
+        promptForPushNotificationsWithUserResponse(handler: (response: boolean) => void): void;
 
         /**
          * Disable the push notification subscription to OneSignal.
@@ -393,4 +393,4 @@ declare module 'react-native-onesignal' {
     }
     const OneSignal: OneSignal;
     export default OneSignal;
-}
+}