indexing: minor edit

Author: Bob Grabar

source/applications/indexes.txt

@@ -152,8 +152,8 @@ create a sorted index on that field.
 
 To sort query results on multiple fields, create a :ref:`compound index
 <index-type-compound>`. MongoDB sorts results based on the field order
-in the index. Ensure that any index constraints on index fields that are
-before the first sort field are equalities.
+in the index. Ensure that any index fields before the first sort field
+are equalities.
 
 .. example::