Fix delicious exception so it is properly eaten

hbmqtt/plugins/manager.py

@@ -140,7 +140,7 @@ class PluginManager:
                     def clean_fired_events(future):
                         try:
                             self._fired_events.remove(task)
-                        except KeyError:
+                        except ValueError:
                             pass
 
                     task.add_done_callback(clean_fired_events)