tweak inmemory

Author: kay-kim

source/core/inmemory.txt

@@ -127,7 +127,7 @@ Durability
 ----------
 
 The in-memory storage engine is non-persistent and does not write data
-to a persistent storage. That non-persisted data includes
+to a persistent storage. Non-persisted data includes
 application data and system data, such as users, permissions, indexes,
 replica set configuration, sharded cluster configuration, etc.