Fix MySQL Replication fatal error 1236

Got fatal error 1236 from master when reading data from binary log:
'The slave is connecting using CHANGE MASTER TO MASTER_AUTO_POSITION = 1, but the master has purged binary logs containing GTIDs that the slave requires.'

mysql> show global variables like 'gtid_purged'; # show master's gtid_purged

mysql> stop slave;
mysql> set global gtid_purged = '3caafe57-7a46-11e6-a5c0-00505682159e:1-50'; # set slave's gtid_purged as master
mysql> reset master;
mysql> start slave;