Update a link to scala/scala3

Author: xerial

docs/_docs/contributing/getting-started.md

@@ -49,7 +49,7 @@ Scala](https://www.jetbrains.com/help/idea/discover-intellij-idea-for-scala.html
 Start by cloning the repository:
 
 ```bash
-$ git clone https://github.com/lampepfl/dotty.git
+$ git clone https://github.com/scala/scala3.git
 $ cd dotty
 ```