Fix NameError in Embed.to_dict

discord/embeds.py

@@ -512,7 +512,7 @@ class Embed:
                 if timestamp.tzinfo:
                     result['timestamp'] = timestamp.astimezone(tz=datetime.timezone.utc).isoformat()
                 else:
-                    result['timestamp'] = timestamp.replace(tzinfo=timezone.utc).isoformat()
+                    result['timestamp'] = timestamp.replace(tzinfo=datetime.timezone.utc).isoformat()
 
         # add in the non raw attribute ones
         if self.type: