[BUG] Sometimes the bot does not display correctly the avatar of the user in an embed

[ItsShunya]

Subject of the issue

In the welcoming messages, the bot sets the thumbnail picture of the embed to the avatar of the user who joined. Sometimes this avatar is not displayed correctly, displaying only a loading screen.

Your environment

• ID: 737219824987406367
• Shuwy version: 0.2.4
• Discord.py version: 1.5.1
• Python version: 3.7.5

Steps to reproduce

Let a member join to a server that has configured the welcome message on member join and add an embed message. Most of the time it will be right, but it will display a loading image some times.

Expected behaviour

The thumbnail picture should be the avatar picture of the user.

Actual behaviour

Sometimes a loading picture gets displayed.

[ItsShunya]

This seems to be a Discord issue related to not being able to retrieve the avatar of the user in cache, similar to #26.
Will look into it, but most likely we should stop using the user's avatar to use a static picture there.