Update Chatters when chatter parts

Chatters will now be removed from cache when a part is received.

Author: chillymosh

docs/changelog.rst

@@ -36,6 +36,7 @@ Master
         - Corrected :class:`~twitchio.Predictor` slots and user keys, repr has also been added
         - Updated IRC parser to not strip colons from beginning of messages
         - Updated IRC parser to not remove multiple spaces when clumped together
+        - Chatters will now update correctly when someone leaves chat
 
 - ext.commands
     - Bug fixes

twitchio/websocket.py

@@ -385,7 +385,10 @@ async def _part(self, parsed):  # TODO
             self._cache.pop(channel, None)
         channel = Channel(name=channel, websocket=self)
         user = Chatter(name=parsed["user"], bot=self._client, websocket=self, channel=channel, tags=parsed["badges"])
-
+        try:
+            self._cache[channel.name].discard(user)
+        except KeyError:
+            pass
         self.dispatch("part", user)
 
     async def _privmsg(self, parsed):  # TODO(Update Cache properly)