Update link to Firebase Android SDK API reference

Author: ChristianKatzmann

README.md

@@ -5,7 +5,7 @@
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 <br/>
 The Firebase Kotlin SDK is a Kotlin-first SDK for Firebase. It's API is similar to the 
-<a href="https://firebase.github.io/firebase-android-sdk/reference/kotlin/firebase-ktx/">Firebase Android SDK Kotlin Extensions</a> 
+<a href="https://firebase.google.com/docs/reference/kotlin/packages">Firebase Android SDK Kotlin Extensions</a> 
 but also supports multiplatform projects, enabling you to use Firebase directly from your common source targeting 
 <strong>iOS</strong>, <strong>Android</strong>, <strong>Desktop</strong> or <strong>Web</strong>, enabling the use of 
 Firebase as a backend for <a href="https://www.jetbrains.com/lp/compose-multiplatform/">Compose Multiplatform</a>, for example.