Fix typo in function name (mongodb#96)

Author: jordan-smith721

source/write/insert.txt

@@ -134,7 +134,7 @@ not customize the insert.
          fields </reference/command/insert/#command-fields>` guide in the
          {+mdb-server+} manual for more information.
 
-The ``InsertMany()`` method accepts the preceding optional parameters,
+The ``insert_many()`` method accepts the preceding optional parameters,
 as well as the optional ``ordered`` property:
 
 .. list-table::