Update GrünstromIndex, new link

README.md

@@ -708,7 +708,7 @@ API | Description | Auth | HTTPS | CORS |
 | [Cloverly](https://www.cloverly.com/carbon-offset-documentation) | API calculates the impact of common carbon-intensive activities in real time | `apiKey` | Yes | Unknown |
 | [CO2 Offset](https://co2offset.io/api.html) | API calculates and validates the carbon footprint | No | Yes | Unknown |
 | [Danish data service Energi](https://www.energidataservice.dk/) | Open energy data from Energinet to society | No | Yes | Unknown |
-| [GrünstromIndex](https://www.corrently.de/hintergrund/gruenstromindex/index.html) | Green Power Index for Germany (Grünstromindex/GSI) | No | No | Yes |
+| [GrünstromIndex](https://gruenstromindex.de/) | Green Power Index for Germany (Grünstromindex/GSI) | No | No | Yes |
 | [IQAir](https://www.iqair.com/air-pollution-data-api) | Air quality and weather data | `apiKey` | Yes | Unknown |
 | [La Data Verte](https://ladataverte.fr) | Aggregation of multiple environmental indicators (CO2 emissions, Average temperature, etc) | No | Yes | Unknown |
 | [Luchtmeetnet](https://api-docs.luchtmeetnet.nl/) | Predicted and actual air quality components for The Netherlands (RIVM) | No | Yes | Unknown |