Timeout the pubIp env variable set in container

[navilg]

Currently when IP address is set in namecheap, ncddns sets an env variable in current container so that it can compare the next time with current public IP. It prints the message "DNS record is same as current IP" if current public IP and env variable set is same.

This may not work if someone changes the IP address of a dns from namecheap dashboard unless container is restarted again. To avoid this, We can have a timeout set for env variable set, after which it should be wiped out so that fresh attempt to add ip address is made by ncddns.