Restore Optional Target Config Attribute (notify.pushover) (#3769)

* Restore Optional Target Config Attribute

* Fix Tabs

* Change indents to spaces

* Make a target fix

* Change to simpler not syntax

homeassistant/components/notify/pushover.py

@@ -63,6 +63,9 @@ class PushoverNotificationService(BaseNotificationService):
 
         targets = kwargs.get(ATTR_TARGET)
 
+        if not isinstance(targets, list):
+            targets = [targets]
+
         for target in targets:
             if target is not None:
                 data['device'] = target