typo revisited: there is only one procedure in this topic

Author: Bob Grabar

source/tutorial/convert-standalone-to-replica-set.txt

@@ -23,7 +23,7 @@ administration </replication>`, see:
 Procedure
 ---------
 
-These procedures assume you have a :term:`standalone` instance of MongoDB
+This procedure assumes you have a :term:`standalone` instance of MongoDB
 installed. If you have not already installed MongoDB, see the
 :ref:`installation tutorials <tutorials-installation>`.