Fix hyperlink on the https://docs.datastax.com/en/developer/java-driver/latest/manual/mapper/mapper/#mapper-builder website (#1723)

diff --git a/manual/mapper/mapper/README.md b/manual/mapper/mapper/README.md
index 18be59d..894143f 100644
--- a/manual/mapper/mapper/README.md
+++ b/manual/mapper/mapper/README.md
@@ -39,7 +39,7 @@
 ```
 
 The builder allows you to create a mapper instance, by wrapping a core `CqlSession` (if you need
-more details on how to create a session, refer to the [core driver documentation](../core/)).
+more details on how to create a session, refer to the [core driver documentation](../../core/)).
 
 ```java
 CqlSession session = CqlSession.builder().build();