Update Dota 2 API authentication (#1711)

README.md

@@ -454,7 +454,7 @@ API | Description | Auth | HTTPS | CORS |
 | [Dark Souls 3](https://blog.mugenmonkey.com/2017/09/10/ds3-api.html) | Information about Dark Souls 3 Items | No | Yes | Unknown |
 | [Deck of Cards](http://deckofcardsapi.com/) | Deck of Cards | No | No | Unknown |
 | [Destiny The Game](https://github.com/Bungie-net/api) | Bungie Platform API | `apiKey` | Yes | Unknown |
-| [Dota 2](https://docs.opendota.com/) | Provides information about Player stats , Match stats, Rankings for Dota 2 | No | Yes | Unknown |
+| [Dota 2](https://docs.opendota.com/) | Provides information about Player stats , Match stats, Rankings for Dota 2 | `apiKey` | Yes | Unknown |
 | [Dungeons and Dragons](http://www.dnd5eapi.co/) | Reference for 5th edition spells, classes, monsters, and more | No | No | No |
 | [Eve Online](https://esi.evetech.net/ui) | Third-Party Developer Documentation | `OAuth` | Yes | Unknown |
 | [FIFA Ultimate Team](https://www.easports.com/fifa/ultimate-team/api/fut/item) | FIFA Ultimate Team items API | No | Yes | Unknown |