Don't try to remove managed roles (#170)

dungeon/dungeon.py

@@ -72,8 +72,10 @@ class Dungeon(commands.Cog):
         if not dungeon_role_obj:
             return await ctx.send("No dungeon role set.")
 
+        #Managed roles CANNOT be removed by the bot.
+        remaining_roles = [r for r in user.roles if r.managed]
         try:
-            await user.edit(roles=[], reason=f"Removing all roles, {ctx.message.author} is banishing user")
+            await user.edit(roles=remaining_roles, reason=f"Removing all roles, {ctx.message.author} is banishing user")
         except discord.Forbidden:
             return await ctx.send(
                 "I need permission to manage roles or the role hierarchy might not allow me to do this. I need a role higher than the person you're trying to banish."