Fixed "retail" being swapped with "MongoDB"

Author: mutewinter

source/use-cases/product-catalog.txt

@@ -360,8 +360,8 @@ order of the index does not matter.
 .. note::
 
    If you want to preform range queries (e.g. "return all products
-   over $25") and then sort by another property like ``pricing.MongoDB``,
-   retail cannot use the index as effectively in this situation.
+   over $25") and then sort by another property like ``pricing.retail``,
+   MongoDB cannot use the index as effectively in this situation.
 
    The field that you want to select a range, or perform sort
    operations, must be the *last* field in a compound index in order