Added fix for ios target, there was a typo in collectionGroupWithID (#144)

Author: Reedyuk

firebase-firestore/src/iosMain/kotlin/dev/gitlive/firebase/firestore/firestore.kt

@@ -42,7 +42,7 @@ actual class FirebaseFirestore(val ios: FIRFirestore) {
 
     actual fun collection(collectionPath: String) = CollectionReference(ios.collectionWithPath(collectionPath))
 
-    actual fun collectionGroup(collectionId: String) = Query(ios.collectionGroupWithId(collectionId))
+    actual fun collectionGroup(collectionId: String) = Query(ios.collectionGroupWithID(collectionId))
 
     actual fun document(documentPath: String) = DocumentReference(ios.documentWithPath(documentPath))