title: discord.py rewrite: TypeError: cogs must derive from Cog
body: <p>As my bot is getting bigger, I'm trying to implement cogs, however I have ran across a problem. I have my whole code set up and ready, but for some weird reason I keep getting this error:</p>
  
  <pre><code>    Traceback (most recent call last):
    File "C:\Users\Lauras\Desktop\Akagi Bot\main.py", line 107, in &lt;module&gt;
      bot.add_cog("cogs.fun")
    File "C:\Users\Lauras\AppData\Local\Programs\Python\Python36\lib\site-packages\discord\ext\commands\bot.py", line 477, in add_cog
      raise TypeError('cogs must derive from Cog')
  TypeError: cogs must derive from Cog
  </code></pre>
  
  <p>My code on main.py looks like this:</p>
  
  <pre><code>   import discord
      import asyncio
      import typing
      import random
      import json
      import oauth
      from discord.ext import commands
  
  bot = commands.Bot(command_prefix='~')
  
  @bot.event
  async def on_ready():
      await bot.change_presence(activity=discord.Activity(name='with Kaga :3',type=0))
      print (discord.__version__)
      print(f"{bot.user.name} - {bot.user.id}")
      print ('Akagi is ready to serve the Commander :3 !')
  
      bot.add_cog("cogs.fun")
      bot.run(oauth.bot_token)
  </code></pre>
  
  <p>And the "fun" cog is as follows:</p>
  
  <pre><code>import discord
  from discord.ext import commands
  
  bot = commands.Bot(command_prefix='~')
  
  class FunCog:
      def __init__(self, bot):
          self.bot = bot
  
      @commands.command()
      async def hug(self, ctx):
          await ctx.send('has been hugged by', file=discord.File('iloveyou.gif'))
          pass
  
  
  def setup(bot: commands.Bot):
      bot.add_cog(FunCog(bot))
  </code></pre>
  
  <p>What could be the problem? I'm also using discord.py rewrite. Thanks !</p>