[Dungeon] update the listener too

dungeon/dungeon.py

@@ -345,7 +345,7 @@ class Dungeon(commands.Cog):
         embed = discord.Embed(colour=ctx.guild.me.top_role.colour, description=msg)
         return await ctx.send(embed=embed)
 
-    @listener()
+    @commands.Cog.listener()
     async def on_member_join(self, member):
         default_avatar = False
         toggle = await self.config.guild(member.guild).toggle()