Update README.md

Changed "Zippopotam" to the full name of the service: "Zippopotam.us" (rhymes with hippopotamus)

README.md

@@ -461,7 +461,7 @@ API | Description | Auth | HTTPS | CORS |
 | [Utah AGRC](https://api.mapserv.utah.gov) | Utah Web API for geocoding Utah addresses | `apiKey` | Yes | Unknown |
 | [ViaCep](https://viacep.com.br) | Brazil RESTful zip codes API | No | Yes | Unknown |
 | [ZipCodeAPI](https://www.zipcodeapi.com) | US zip code distance, radius and location API | `apiKey` | Yes | Unknown |
-| [Zippopotam](http://www.zippopotam.us) | Get information about place such as country, city, state, etc | No | No | Unknown |
+| [Zippopotam.us](http://www.zippopotam.us) | Get information about place such as country, city, state, etc | No | No | Unknown |
 
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 ### Government