Fix startAt, endAt, equalTo optional 2nd params on Android

[BlooJeans]

Fixes

E/unknown:React: Exception in native call
                 java.lang.ArrayIndexOutOfBoundsException: length=2; index=2
                     at io.fullstack.firestack.FirestackDBReference.getDatabaseQueryAtPathAndModifiers(FirestackDatabase.java:235)
                     at io.fullstack.firestack.FirestackDBReference.addChildEventListener(FirestackDatabase.java:90)
                     at io.fullstack.firestack.FirestackDatabaseModule.on(FirestackDatabase.java:379)
                     at java.lang.reflect.Method.invoke(Native Method)
                     at com.facebook.react.bridge.BaseJavaModule$JavaMethod.invoke(BaseJavaModule.java:319)
                     at com.facebook.react.cxxbridge.JavaModuleWrapper.invoke(JavaModuleWrapper.java:158)
                     at com.facebook.react.bridge.queue.NativeRunnable.run(Native Method)
                     at android.os.Handler.handleCallback(Handler.java:751)
                     at android.os.Handler.dispatchMessage(Handler.java:95)
                     at com.facebook.react.bridge.queue.MessageQueueThreadHandler.dispatchMessage(MessageQueueThreadHandler.java:31)
                     at android.os.Looper.loop(Looper.java:154)
                     at com.facebook.react.bridge.queue.MessageQueueThreadImpl$3.run(MessageQueueThreadImpl.java:196)
                     at java.lang.Thread.run(Thread.java:761)