`set` and `expire` api diffrent handle to 'expire time' param

[lvsoso]

expire:

redis-py/redis/commands/core.py

Line 1592 in 42b937f

def expire(

set:

redis-py/redis/commands/core.py

Line 2175 in 42b937f

raise DataError("ex must be datetime.timedelta or int")

The set api ex should be a interger, but expire's time can use a string(integer in string type) as input.

It make me confusing. Both can also accept string type is more convenient.