Update sample4.cs (#4859)

* Update sample4.cs

In OWIN version 4.0 (prerelease) you cannot compare string with Path directly. You must get its value first

* Update sample4.cs

aspnet/aspnet/overview/owin-and-katana/getting-started-with-owin-and-katana/samples/sample4.cs

@@ -6,7 +6,7 @@ public void Configuration(IAppBuilder app)
     app.Run(context =>
     {
         // New code: Throw an exception for this URI path.
-        if (context.Request.Path == "/fail")
+        if (context.Request.Path.Equals(new PathString("/fail")))
         {
             throw new Exception("Random exception");
         }