Fix uses of super() in the codebase

Fix #3165, we don’t need to use the long form to get the superobject in
our supported python versions.

examples/pubsub_client.py

@@ -15,7 +15,7 @@ class PubsubClient(slixmpp.ClientXMPP):
 
     def __init__(self, jid, password, server,
                        node=None, action='nodes', data=''):
-        super(PubsubClient, self).__init__(jid, password)
+        super().__init__(jid, password)
 
         self.register_plugin('xep_0030')
         self.register_plugin('xep_0059')

examples/pubsub_events.py

@@ -14,7 +14,7 @@ from slixmpp.xmlstream.handler import Callback
 class PubsubEvents(slixmpp.ClientXMPP):
 
     def __init__(self, jid, password):
-        super(PubsubEvents, self).__init__(jid, password)
+        super().__init__(jid, password)
 
         self.register_plugin('xep_0030')
         self.register_plugin('xep_0059')

examples/user_location.py

@@ -22,7 +22,7 @@ from slixmpp import ClientXMPP
 class LocationBot(ClientXMPP):
 
     def __init__(self, jid, password):
-        super(LocationBot, self).__init__(jid, password)
+        super().__init__(jid, password)
 
         self.add_event_handler('session_start', self.start)
         self.add_event_handler('user_location_publish',

examples/user_tune.py

@@ -17,7 +17,7 @@ from slixmpp import ClientXMPP
 class TuneBot(ClientXMPP):
 
     def __init__(self, jid, password):
-        super(TuneBot, self).__init__(jid, password)
+        super().__init__(jid, password)
 
         # Check for the current song every 5 seconds.
         self.schedule('Check Current Tune', 5, self._update_tune, repeat=True)