allow to reconnect, i experience dissconnect error multiple times

[bokunodev]

i experienced this alot pymysql.err.OperationalError: (2013, 'Lost connection to MySQL server during query')
and i think this change will fix it.

PyMySQLPool/pymysqlpool/pool.py

Line 184 in 212110a

c.ping()

change to c.ping(reconnect=True)