[lint] Replace deprecated Logger function warn
[lint] Replace deprecated Logger function warn

The method log of Logger has never been documented as being a part of
the standard logging module.  It was renamed to warning when the module
was included in the standard library, but the old name was kept for
backward compatibility.

Harmon758/discord.py,imayhaveborkedit/discord.py,Harmon758/discord.py,khazhyk/discord.py,Rapptz/discord.py,rapptz/discord.py