Another minor correction on getting started page

Author: puentesarrin

source/tutorial/getting-started.txt

@@ -177,7 +177,7 @@ Insert Individual Documents
 
       db.things.find()
 
-   This operation returns the returns the following results. The :doc:`ObjectId
+   This operation returns the following results. The :doc:`ObjectId
    </core/object-id>` values will be unique:
 
    .. code-block:: javascript