DOCSP-50497 Fix bold bullet point

Author: mballard-mdb

source/aggregation.txt

@@ -97,8 +97,9 @@ Consider the following :manual:`limitations </core/aggregation-pipeline-limits/>
   property of the ``AggregateOptions`` object that you pass to the
   ``Aggregate()`` method. 
 
-- The :ref:`$graphLookup </reference/operator/aggregation/graphLookup/>` stage has a strict memory
-   limit of 100 megabytes and will ignore the ``AllowDiskUse`` property.
+- The :manual:`$graphLookup </reference/operator/aggregation/graphLookup/>`
+  stage has a strict memory limit of 100 megabytes and will ignore the
+  ``AllowDiskUse`` property.
 
 Aggregation Example
 -------------------