Fix lang typo

htdocs/langs/en_US/products.lang

@@ -244,6 +244,6 @@ MinimumPriceLimit=Minimum price can't be lower that %s
 MinimumRecommendedPrice=Minimum recommended price is : %s
 PriceExpressionEditor=Price expression editor
 PriceExpressionSelected=Selected price expression
-PriceExpressionEditorHelp="price = 2 + 2" or "2 + 2" for setting the price<br>ExtraFields are variables like "#options_myextrafieldkey# * 2"<br>There are special variables like "quantity" and "tva_tx"
+PriceExpressionEditorHelp="price = 2 + 2" or "2 + 2" for setting the price<br>ExtraFields are variables like "#options_myextrafieldkey# * 2"<br>There are special variables like #quantity# and #tva_tx#
 PriceMode=Price mode
 PriceNumeric=Number