Please use another bitcoin fees API provider

Hi, I'm not familiar with your project. I did a search for `https://bitcoinfees.earn.com/api/v1/fees/recommended` and am alerting projects using this API to inaccurate & old data.

An up-to-date API with accurate data would be `https://mempool.space/api/v1/fees/recommended` or some alternative.

https://github.com/OpenBazaar/feeproxy/blob/1300b725c8be019dd084de359827cb3ad36ae0df/main.go