Update popup_url variable

Edit from "test:/test/PopupTest.html"; to "test://test/PopupTest.html";

Author: oknoorap

CefSharp.Example/ExamplePresenter.cs

@@ -23,7 +23,7 @@ public static void Init()
         private const string scheme_url = "test://test/SchemeTest.html";
         private const string bind_url = "test://test/BindingTest.html";
         private const string tooltip_url = "test://test/TooltipTest.html";
-        private const string popup_url = "test:/test/PopupTest.html";
+        private const string popup_url = "test://test/PopupTest.html";
 
         private int color_index = 0;
         private readonly string[] colors =