Get Activity from RN Context

• Changes how the SDK gets a reference to the current activity during initialization

Author: Nightsd01

android/src/main/java/com/geektime/rnonesignalandroid/RNOneSignal.java

@@ -105,7 +105,7 @@ private JSONObject jsonFromErrorMessageString(String errorMessage) throws JSONEx
 
    @ReactMethod 
    public void init(String appId) {
-      Activity activity = getCurrentActivity();
+      Activity activity = mReactApplicationContext.getCurrentActivity();
 
       if (activity == null) {
          // in some cases, especially with react-native-navigation, it can take a while for the Activity to be created