Fix the link to Transport for Berlin, Germany API (#1158)

README.md

@@ -874,7 +874,7 @@ API | Description | Auth | HTTPS | CORS |
 | [Transport for Atlanta, US](http://www.itsmarta.com/app-developer-resources.aspx) | Marta | No | No | Unknown |
 | [Transport for Auckland, New Zealand](https://api.at.govt.nz/) | Auckland Transport | No | Yes | Unknown |
 | [Transport for Belgium](https://hello.irail.be/api/) | Belgian transport API | No | Yes | Unknown |
-| [Transport for Berlin, Germany](https://github.com/derhuerst/vbb-rest/blob/master/docs/index.md) | Third-party VBB API | No | Yes | Unknown |
+| [Transport for Berlin, Germany](https://github.com/derhuerst/vbb-rest/blob/3/docs/index.md) | Third-party VBB API | No | Yes | Unknown |
 | [Transport for Bordeaux, France](https://opendata.bordeaux-metropole.fr/explore/) | Bordeaux Métropole public transport and more (France) | `apiKey` | Yes | Unknown |
 | [Transport for Boston, US](https://mbta.com/developers/v3-api) | MBTA API | No | No | Unknown |
 | [Transport for Budapest, Hungary](https://bkkfutar.docs.apiary.io) | Budapest public transport API | No | Yes | Unknown |