Allow DM commands

Robocop.py

@@ -149,7 +149,7 @@ async def on_message(message):
     if message.author.bot:
         return
 
-    if message.guild.id not in config.guild_whitelist:
+    if (message.guild) and (message.guild.id not in config.guild_whitelist):
         return
 
     ctx = await bot.get_context(message)