databases/py-mysqlclient: update to 2.0.1 release

• Dropped Python 2 support
• Dropped Django 1.11 support
• Add context manager interface to Connection which closes the connection on `__exit__`.
• Add `ssl_mode` option.
• Fixed multithread safety issue in fetching row.
• Removed obsolete members from Cursor. (e.g. messages, _warnings, _last_executed)