fix syntax

Author: Chris Cho

source/style-guide/markup/directives/sharedinclude.txt

@@ -149,7 +149,7 @@ in the ``sharedinclude`` directive:
 
    .. sharedinclude:: dbx/fundamentals/agg-operators.rst
 
-      .. replacement::
+      .. replacement:: learn-agg-operator-docs
 
          Aggregation Operations page in the
          :server:`MongoDB Server documentation </aggregation>`