Fix regression with string/toString

Author: niftynei

app/src/main/java/com/zulip/android/networking/AsyncGetEvents.java

@@ -112,7 +112,7 @@ private void register() throws JSONException, IOException {
 
         watch.reset();
         watch.start();
-        JSONObject response = new JSONObject(responseData.body().toString());
+        JSONObject response = new JSONObject(responseData.body().string());
         watch.stop();
         Log.i("perf", "json: v1/register: " + watch.toString());