Update shell-types.txt

grammar fix

Author: kerneljake

source/core/shell-types.txt

@@ -69,7 +69,7 @@ The operation returns ``string``.
 Return ``Date``
 ```````````````
 
-The :program:`mongo` shell wrap objects of ``Date`` type with the
+The :program:`mongo` shell wraps objects of ``Date`` type with the
 ``ISODate`` helper; however, the objects remain of type ``Date``.
 
 The following example uses both the ``new Date()`` constructor and the