use new deletedir api

build.cake

@@ -95,7 +95,10 @@ Task("Clean")
 	{
         if (DirectoryExists(artifactsDir))
         {
-            DeleteDirectory(artifactsDir, recursive:true);
+            DeleteDirectory(artifactsDir, new DeleteDirectorySettings {
+				Recursive = true,
+				Force = true
+			});
         }
         CreateDirectory(artifactsDir);
 	});