added ratesapi.io to Currency Exchange (#902)

README.md

@@ -210,6 +210,7 @@ API | Description | Auth | HTTPS | CORS |
 | [Czech National Bank](https://www.cnb.cz/cs/financni_trhy/devizovy_trh/kurzy_devizoveho_trhu/denni_kurz.xml) | A collection of exchange rates | No | Yes | Unknown |
 | [Exchangeratesapi.io](https://exchangeratesapi.io) | Exchange rates with currency conversion | No | Yes | Yes |
 | [Fixer.io](http://fixer.io) | Exchange rates and currency conversion | `apiKey` | Yes | Unknown |
+| [ratesapi](https://ratesapi.io) | Free exchange rates and historical rates | No | Yes | Unknown |
 
 ### Data Validation
 API | Description | Auth | HTTPS | CORS |