Discord.py dep update 3.1 (#2587)

* Dependency update

discord.py==1.0.1
websockets<7

[style]
black==19.3b0

[Docs]
jinja==2.10.1
urllib3==1.24.2

Changes related to breaking changes from discord.py have also been made
to match

As of this commit, help formatter is back to discord.py's default

redbot/cogs/customcom/customcom.py

@@ -434,6 +434,7 @@ class CustomCommands(commands.Cog):
         for p in pagify(text):
             await ctx.send(box(p, lang="yaml"))
 
+    @commands.Cog.listener()
     async def on_message(self, message):
         is_private = isinstance(message.channel, discord.abc.PrivateChannel)