Fix Fetching Data example (#403)

docs/integration_fetching_data.md

@@ -28,9 +28,10 @@ This API will have a single method to fetch data for all the entities that you h
 Home Assistant provides a DataUpdateCoordinator class to help you manage this as efficiently as possible.
 
 ```python
+from datetime import timedelta
 import logging
 
-from homeassistant.helpers import debounce, entity
+from homeassistant.helpers import entity
 from homeassistant.helpers.update_coordinator import DataUpdateCoordinator, UpdateFailed
 from .const import DOMAIN
 
@@ -90,7 +91,7 @@ class MyEntity(entity.Entity):
     @property
     def available(self):
         """Return if entity is available."""
-        return not self.coordinator.failed_last_update
+        return self.coordinator.last_update_success
 
     async def async_added_to_hass(self):
         """When entity is added to hass."""