DOCS-941: clarifying versions in chained replication

Author: Sam Kleinman

source/administration/replica-sets.txt

@@ -355,7 +355,7 @@ the event of a network partition.
 Chained Replication
 ~~~~~~~~~~~~~~~~~~~
 
-.. versionadded:: 2.4
+.. versionadded:: 2.0
 
 Chained replication occurs when a :term:`secondary` member replicates
 from another secondary member instead of from the :term:`primary`. This