MAGETWO-44415: Impossible edit tax rate from "New Tax Rule" page

- fixed the open command for the new js modal to openModal

Author: Partica, Cristian

app/code/Magento/Tax/view/adminhtml/templates/rule/edit.phtml

@@ -88,7 +88,7 @@ require([
                         item.itemElement = that.prev();
                         $('#tax-rate-form')
                             .dialogRates({itemRate: item})
-                            .dialogRates('open');
+                            .dialogRates('openModal');
 
                     } else {
                         if (result.error_message)