Fix voice state update issue in on_voice_state_update

Bug was caused to the shallow copy not copying over the VoiceState
information embedded into the copy. This would mean that when the event
is called, before and after voice state information is essentially
equivalent.

The solution to fix this is to also copy the VoiceState objects.

discord/server.py

@@ -31,7 +31,6 @@ from .game import Game
 from .channel import Channel
 from .enums import ServerRegion, Status
 from .mixins import Hashable
-import copy
 
 class Server(Hashable):
     """Represents a Discord server.
@@ -137,8 +136,9 @@ class Server(Hashable):
     def _update_voice_state(self, data):
         user_id = data.get('user_id')
         member = self.get_member(user_id)
-        before = copy.copy(member)
+        before = None
         if member is not None:
+            before = member._copy()
             ch_id = data.get('channel_id')
             channel = self.get_channel(ch_id)
             member._update_voice_state(voice_channel=channel, **data)