updated dependencies, command error only gets raised on longer messages

updated to new breaking changes in discord.py 2.0a

fixed on_guild_join() method

forgot to install git in the docker build

updated to Python 3.9 and Discord.py 2.0 Alpha

fixed the bug whwich broke the :nsfw command

changed the way how the bot detects it is run via docker \n version b…

…umps of websockets to version 9.1

version bump to discord.py 1.7.2

replaced client.logout() with client.close() since it is now declared…

… deprecated since discord.py 1.7

DISCORD_SELFASSIGNROLE and __selfassignrole__ works again