Use self.trigger instead of self._trigger

Author: blag

contrib/linux/sensors/file_watch_sensor.py

@@ -221,7 +221,7 @@ def add_trigger(self, trigger):
 
         self.trigger = trigger.get('ref', None)
 
-        if not self._trigger:
+        if not self.trigger:
             raise Exception('Trigger %s did not contain a ref.' % trigger)
 
         self.tail_manager.tail_file(file_path, self._handle_line)