Change default pool to public-pool.io

[ffrediani]

Hello

The default pool set pool.vkbit.com have gone through a recent upgrade which made it not usable for low hashrate devices as it does ot show the hashate accurately anymore on the web interface. After discussion with the maintainer in the appropriate support channel he confirmed the changes would not be reverted, that he would rather to privilege higher hashrate devices and advise to move lower hashrate devices to public-pool.io.

Could you then make the default pool for the next release stratum+tcp://public-pool.io:21496 ?

Thanks