Fix integration for HA versions 2021.12.0 or later

As reported in #38, this simple fix should address this problem - and it did for me as well. 

I assume this will not cause problems for folks who use the integration with earlier versions, but it'd be great if someone could check my assumption there!

custom_components/kuna/camera.py

@@ -97,7 +97,7 @@ def device_state_attributes(self):
 
     def update(self):
         """Fetch state data from the updated account camera dict."""
-        self.is_streaming = True
+        self._is_streaming = True
         try:
             self._camera = self._account.account.cameras[self._original_id]
         except KeyError: