Fix to total_seconds missing parens

rocketbot/cogs/crosspostcog.py

 			Storage.set_state_value(message.guild, self.STATE_KEY_RECENT_MESSAGES, recent_messages)
 		recent_messages.max_age = max_age
 		recent_messages.append(message)
-		self.__trace(f"Recent messages now length {len(recent_messages)} (max age {max_age.total_seconds}s)")
+		self.__trace(f"Recent messages now length {len(recent_messages)} (max age {max_age.total_seconds()}s)")
 
 		# Get all recent messages by user
 		member_messages = [m for m in recent_messages if m.author.id == message.author.id]