moved to IPStack before API stops working in July

From https://freegeoip.net/json/:

> This API endpoint is deprecated and will stop working on July 1st, 2018. For more information please visit: https://github.com/apilayer/freegeoip#readme

From https://github.com/apilayer/freegeoip#readme

> After years of operation and the API remaining almost unchanged, today we announce the complete re-launch of freegeoip into a faster, more advanced and more scalable API service called ipstack (https://ipstack.com). All users that wish to continue using our IP to location service will be required to sign up to obtain a free API access key and perform a few simple changes to their integration. While the new API offers the ability to return data in the same structure as the old freegeoip API, the new API structure offers various options of delivering much more advanced data for IP Addresses.