Fix 'date' ref link target on ttl page

Author: jeff-allen-mongo

source/core/index-ttl.txt

@@ -57,8 +57,9 @@ If the field is an array, and there are multiple date values in the
 index, MongoDB uses *lowest* (i.e. earliest) date value in the array to
 calculate the expiration threshold.
 
-If the indexed field in a document is not a :term:`date <BSON types>`
-or an array that holds a date value(s), the document will not expire.
+If the indexed field in a document is not a
+:ref:`date <document-bson-type-date>` or an array that holds one or
+more date values, the document will not expire.
 
 If a document does not contain the indexed field, the document will not
 expire.