weibo created_at format changed and should be adapted

[zbutfly]

Now it's json format like 'Sat Feb 06 01:50:21 +0800 2021', the old date parsing code return 'None' for ever.

The code of parse_date should be:

import dateutil.parser

def parse_date(text):
    return dateutil.parser.parse(text).date()
    # all other line in the function should be removed.

code tested successfully by me.