update net40 example

Author: matiii

src/Samples/Dijkstra.Net40/Program.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Linq;
 using Dijkstra.NET.Contract;
+using Dijkstra.NET.Extensions;
 using Dijkstra.NET.Model;
 using Dijkstra.NET.ShortestPath;
 
@@ -24,13 +25,15 @@ static void Main(string[] args)
 
             graph.Reset();
 
+            var immutablePath = graph.Dijkstra(0, 1);
+
             var bfs = new BfsParallel<int, string>(graph);
 
             IShortestPathResult bfsResult = bfs.Process(0, 1);
 
             var bfsPath = bfsResult.GetPath();
 
-            if (!bfsPath.SequenceEqual(path))
+            if (!bfsPath.SequenceEqual(path) || !immutablePath.GetPath().SequenceEqual(path))
             {
                 throw new Exception("The path should be the same.");
             }