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/mod/movetocore.py

@@ -16,10 +16,12 @@ class MoveToCore(MixinMeta):
     Mixin for things which should really not be in mod, but have not been moved out yet.
     """
 
+    @commands.Cog.listener()
     async def on_command_completion(self, ctx: commands.Context):
         await self._delete_delay(ctx)
 
     # noinspection PyUnusedLocal
+    @commands.Cog.listener()
     async def on_command_error(self, ctx: commands.Context, error):
         await self._delete_delay(ctx)