report a typo in comments of ComputeXidHorizonsResult

[Junwang Zhao]

I think the period here should be a typo.

index 16b5803d388..af3b15e93df 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -185,7 +185,7 @@ typedef struct ComputeXidHorizonsResult
        FullTransactionId latest_completed;

        /*
-        * The same for procArray->replication_slot_xmin and.
+        * The same for procArray->replication_slot_xmin and
         * procArray->replication_slot_catalog_xmin.
         */

-- 
Regards
Junwang Zhao