Solve bindmethod deprecation warning

As mentioned at the jQuery 3.0 upgrade guide [1] the `bind` method is deprecated. Replace with `on` method.

[1] https://jquery.com/upgrade-guide/3.0/#deprecated-bind-and-delegate

app/views/admin/poll/questions/answers/images/destroy.js.erb

@@ -1,3 +1,3 @@
-$(".delete").bind("ajax:success", function () {
+$(".delete").on("ajax:success", function () {
-  $(this).closest("div").fadeOut()
+  $(this).closest("div").fadeOut();
-})
+});