fix reference to incorrect usage of collStats command

Author: jrassi

source/reference/command/collStats.txt

@@ -11,9 +11,9 @@ collStats
 
    .. code-block:: javascript
 
-      { collStats: "database.collection" , scale : 1024 }
+      { collStats: "collection" , scale : 1024 }
 
-   Specify a namespace ``database.collection`` and
+   Specify the ``collection`` you want statistics for, and
    use the ``scale`` argument to scale the output. The above example
    will display values in kilobytes.