Deprecated Fixer.io API

[Lucidiot]

The Fixer.io API currently in use by forex-python is deprecated and will stop working on June 1st. The new API requires a key, free keys only allow 1000 requests/month and EUR as the only base currency.

See the announcement on their GitHub repo: https://github.com/fixerAPI/fixer#readme

[ravigadila]

@Lucidiot
Changed currency source to https://ratesapi.io/api/ in new forex-python version(1.0.0)

https://pypi.org/project/forex-python/