changed quantity from string to double (Azure#8391)

Author: wecha-ms

specification/azsadmin/resource-manager/commerce/Microsoft.Commerce.Admin/preview/2015-06-01-preview/Commerce.json

@@ -198,7 +198,8 @@
         },
         "quantity": {
           "description": "The amount of the resource consumption that occurred in this time frame.",
-          "type": "string"
+          "type": "number",
+          "format": "double"
         },
         "meterId": {
           "description": "Unique ID for the resource that was consumed, for example, the Resource ID.",