minor #4461 Update doctrine.rst (guiguiboy)

This PR was submitted for the 2.5 branch but it was merged into the 2.3 branch instead (closes #4461).

Discussion
----------

Update doctrine.rst

fixed typo

Commits
-------

cb0865d Update doctrine.rst

book/doctrine.rst

@@ -747,8 +747,8 @@ normal ``Query`` object, which can be used to get the result of the query.
     (``:price`` in the example above) as it prevents SQL injection attacks.
 
 The ``getResult()`` method returns an array of results. To get only one
-result, you can use ``getSingleResult()`` (which throws exception there is no
-result) or ``getOneOrNullResult()``::
+result, you can use ``getSingleResult()`` (which throws an exception if there
+is no result) or ``getOneOrNullResult()``::
 
     $product = $query->getOneOrNullResult();