fix typo found in mongodb#1661

Author: Sam Kleinman

source/tutorial/remove-documents.txt

@@ -31,8 +31,8 @@ use the :method:`~db.collection.drop()` method to drop the entire
 collection, including the indexes, and then recreate the collection and
 rebuild the indexes.
 
-Remove Documents that Matches a Condition
------------------------------------------
+Remove Documents that Match a Condition
+---------------------------------------
 
 To remove the documents that match a deletion criteria, call the
 :method:`~db.collection.remove()` method with the ``<query>``