DOCSP-39072 -- fix broken link (#434)

Author: jvincent-mongodb

source/faq.txt

@@ -51,7 +51,7 @@ option or set it to the newly updated major release series.
    update your schema file after the upgrade if you start using
    a newly introduced :manual:`BSON Type </reference/bson-types>`.
 
-   MongoDB 3.4 introduces the :ref:`decimal BSON type <3.4-decimal>`.
+   MongoDB 3.4 introduces the :manual:`decimal BSON type </reference/bson-types>`.
    When you upgrade from MongoDB 3.2 to MongoDB 3.4 and your schema file
    contains ``float64`` values (which map to the ``double`` type in
    MongoDB), you must update your DRDL file after you begin using the