Updating emoji cdn (#137)

Apparently the /api endpoint stopped working, so updating to use the cdn link.

disco/types/guild.py

@@ -72,7 +72,7 @@ class GuildEmoji(Emoji):
 
     @property
     def url(self):
-        return 'https://discordapp.com/api/emojis/{}.{}'.format(self.id, 'gif' if self.animated else 'png')
+        return 'https://cdn.discordapp.com/emojis/{}.{}'.format(self.id, 'gif' if self.animated else 'png')
 
     @cached_property
     def guild(self):