Send PUT data properly in coupon-code.js.coffee

Previously we were sending our data as a query string, instead we should
send it as JSON, since this is a PUT request. This also avoids using the
deprecated Spree.url

frontend/app/assets/javascripts/spree/frontend/checkout/coupon-code.js.coffee

@@ -6,18 +6,18 @@ Spree.onCouponCodeApply = (e) ->
   couponStatus = $("#coupon_status")
   successClass = 'success'
   errorClass = 'alert'
-  url = Spree.url(Spree.routes.apply_coupon_code(Spree.current_order_id),
-    {
-      order_token: Spree.current_order_token,
-      coupon_code: couponCode
-    }
-  )
 
   couponStatus.removeClass([successClass,errorClass].join(" "))
 
+  data =
+    order_token: Spree.current_order_token,
+    coupon_code: couponCode
+
   req = Spree.ajax
-    method: "PUT",
-    url: url
+    method: "PUT"
+    url: Spree.routes.apply_coupon_code(Spree.current_order_id)
+    data: JSON.stringify(data)
+    contentType: "application/json"
 
   req.done (data) ->
     window.location.reload()